Glossary of anatomical structures in the Appendix images

Note: as the brain is largely bilaterally symmetrical, the structures are paired, except for when specifically noted.

Accessory nerve - CN XI, attaches to the lateral aspect of the caudal myelencephalon.

Accessory nerve nucleus - Caudal portion of the nucleus ambiguus in the caudal medulla oblongata, continuous with the motor nucleus of the accessory nerve, which extends through the ventral grey matter of the cervical spinal cord.

Alve(ol)us - Medial aspect of cerebral hemisphere, surrounding the hippocampus. It is white matter comprising efferent fibres arising from the hippocampus and travelling to the fimbria.

Basal nuclei - Collection of deeply located, grey matter in the cerebral hemispheres, lateral to the lateral ventricles. They function with the extrapyramidal motor system and are primarily concerned with the execution of voluntary posture and movement.

Basilar artery - Artery on the ventral aspect of the brainstem connecting the paired vertebral arteries with the cerebral arterial circle. The direction of blood flow is species-specific.

Body of the fornix - White matter between the rostral aspects of the paired, lateral ventricles. The axons from hippocampal neurons form the rostrally-directed, paired crura of the fornix, and meet on the midline to form the body of the fornix between the lateral ventricles.

Brachium of the caudal colliculus - White matter located on the dorsolateral aspect of the midbrain. The brachium conveys auditory afferent fibres from the caudal colliculus of the mesencephalon to the rostral colliculus (origin of the tectospinal tract) and to the medial geniculate nucleus of the diencephalon.

Brachium of the rostral colliculus - White matter of the dorsomedial aspect of midbrain, conveying axons from the optic tract and visual cortex to the rostral colliculus.

Callosal sulcus - The sulcus on the medial aspect of the cerebral hemisphere, at the base of the longitudinal fissure. It separates the corpus callosum from the cingulate gyrus.

Caudal cerebellar peduncle - Bidirectional bundle of fibres connecting the cerebellum to the myelencephalon. They convey proprioceptive information from the dorsal spinocerebellar, cuneocerebellar and cervicospinocerebellar tracts to the cerebellum: also the climbing fibres from the olivary nucleus. Efferent fibres from the fastigial nucleus exit via this peduncle travelling to the vestibular and reticular formation in the medulla oblongata. The medial aspect (juxtarestiform body) connects bidirectionally between the vestibulocerebellum and vestibular nuclei of the myelencephalon.

Caudal colliculus - Protuberance on the caudodorsal mesencephalon (tectum); associated with auditory function and reflex head movement.

Caudal commissure - Caudal diencephalon; connects bilaterally between structures of the caudal thalamus and midbrain; it is associated with the pupillary light reflex.

Caudal lobe of cerebellum - Caudal portion of the cerebellum, separated from the rostral lobe by the dorsally located, primary fissure.

Caudal vestibular nucleus - Medial side of the caudal cerebellar peduncle, see Vestibular nuclei.

Caudate nucleus - Rostral, cerebral hemispheres, ventrolateral to the lateral ventricles. It is one of the basal nuclei and functions in the extrapyramidal system.

Central canal - Remnant of the embryonic neural canal, extending the length of the spinal cord. It is filled with CSF and continuous with the caudal aspect of the fourth ventricle.

Central grey matter of mesencephalon (periaqueductal grey) - Grey matter surrounding the mesencephalic aqueduct. It plays a role in the descending modulation of pain, and in defensive behaviour.

Centrum semiovale - Cerebral white matter deep to the cerebral cortex at the junction between the corona radiata and the corpus callosum

Cerebellar cortex - Tightly folded external layer of the cerebellum consisting of the granular, Purkinje and molecular cell layers.

Cerebellar hemisphere - Paired lateral portions of the cerebellum. Primarily functions in coordinating muscle activity in the limbs.

Cerebellar hemisphere, ansiform lobule - Lateral lobule of the cerebellar hemisphere.

Cerebellar hemisphere, dorsal paraflocculus - Dorsal component of a lobule on the ventrolateral aspect of the cerebellar hemisphere.

Cerebellar hemisphere, paramedian lobule - lobule just lateral to the vermis of the caudal lobe.

Cerebellar hemisphere, ventral paraflocculus - Ventral component of a lobule on the ventrolateral aspect of the cerebellar hemisphere, just dorsal to the flocculus.

Cerebellar peduncle - White matter bundles connecting bidirectionally between the cerebellum and the rostral medulla oblongata. The caudal, middle and rostral peduncles converge at the confluence of the cerebellar peduncles.

Cerebellar vermis - Midline portion of the cerebellum. It primarily functions in coordinating axial musculature. It comprises lobules of the rostral lobe (lingula, central, culmen), the primary fissure on the dorsal aspect, caudal lobe (declive, folium, tuber, pyramis, uvula), uvulonodular fissure on the caudoventral aspect and the nodulus.

Cerebellar white matter - Deep to the cerebellar cortex, forms the arbor vitae and contains the deep cerebellar nuclei.

Cerebral arterial circle - Anastomotic circle of arteries on the ventral aspect of the forebrain and midbrain, supplying blood to these regions. Input to, and direction of flow from, the circle is species-specific.

Cerebral peduncle - Prominent paired bundles of fibres extending longitudinally on the ventral aspect of the midbrain, comprising the mesencephalic tegmentum, substantia nigra and crus cerebri.

Choroid fissure - Subarachnoid space surrounding the diencephalon and separating it from the hippocampus. Dorsally it extends rostrally under the fornix. It is separated from the dorsal aspect of the third ventricle by a thin roof plate, which forms the site of attachment of the choroid plexus.

Choroid plexus - Vascular structures in the ventricles of the brain comprising modified ependymal cells and clustered capillaries forming villi; the plexi are the main site of cerebrospinal fluid production.

Cingulate gyrus - Medial aspect of cerebral hemispheres, dorsal to corpus callosum. It is part of the limbic system. It has connections with the parahippocampal gyrus, neocortex and rostral thalamus.

Claustrum - One of the basal nuclei, lateral to the putamen.

Cochlear nuclei - Collections of neurons on the lateral aspects of the rostral medulla oblongata where CN VIII attaches. They receive input from the cochlear nerve, conveying auditory information from the cochlear of the inner ear. Many efferent fibres from the cochlear nuclei decussate forming the trapezoid body and then project rostrally via the lateral lemniscus to synapse in the medial geniculate nucleus. From there they project to the auditory cortex. Other efferent fibres make multiple connections in the brainstem for reflex function.

Columns of the fornix - Medial aspect of the rostral cerebral hemispheres, ventral to the genu of corpus callosum. The columns originate from the body of the fornix and descend ventrally to split at the rostral commissure forming the smaller, pre- and larger, post-commissural fornix. These columns pass into the septal area or the mammillary bodies, respectively.

Commissure - Join between two related structures (commissura - Latin = a meeting or joining together).

Commissure of the hippocampus (commissure of the fornix) - Transverse fibres connecting the left and right fornix of the hippocampus.

Commissure of the rostral colliculus - Axons connecting the left and right rostral colliculi.

Corona radiata - Bidirectional white matter of the telencephalon, dorsal to the level of the caudate nucleus; it radiates into each cerebral gyrus.

Coronal sulcus - Sulcus on the dorsolateral aspect of the rostral third of the cerebral cortex. It is the rostral extension of the marginal sulcus and may be considered to separate the motor and somatosensory cortices.

Corpus callosum - At the base of the longitudinal fissure of the telencephalon. It is the principal white matter commissure joining the left and right cerebral hemispheres. It is only present in placental mammals.

Corpus striatum - Located deep in the telencephalon, ventrolateral to the lateral ventricles. It comprises most of the basal nuclei and intervening white matter; that is caudate nucleus and its ventral extension, the nucleus accumbens, the lentiform nuclei (putamen and the globus pallidus) and claustrum with the internal and external capsules of white matter. The name refers to the striated appearance produced by connected bands of grey substance alternating with the intervening white matter. It is involved in voluntary posture and movement and selectively inhibits and controls motor output from the forebrain.

Cruciate sulcus - Major sulcus in the dorsal frontal lobe. On the dorsal aspect, it forms a cross with the longitudinal fissure. It extends ventrally on the medial surface of the cerebral hemisphere. It is found in some mammals and is the equivalent of the central sulcus in primates. The motor cortex surrounds the cruciate sulcus.

Crus cerebri - Longitudinal bulges that extend along the ventral aspect of the midbrain. They comprise the corticospinal, corticopontine, corticonuclear and corticoreticular fibres. They continue rostrally as the

internal capsule, and caudally as the longitudinal fibres of the pons.

Crus of the fornix - Medial telencephalon, just ventral to the corpus callosum. These white matter fibres connect with the hippocampus and project to the body of the fornix.

Decussation of the pons - Region on the ventral midline of the pons where axons from the pontine nuclei decussate, before ascending through the middle cerebellar peduncle to the cerebellum. It is part of the corticopontocerebellar pathway.

Decussation of the pyramids - Crossing over of corticospinal tracts at the spinomedullary junction on the ventral aspect.

Decussation of the trochlear nerve - CN IV is the only cranial nerve that emerges from the brainstem dorsally, and the only cranial nerve that decussates to innervate the contralateral side. The decussation occurs dorsally, caudal to the caudal colliculi under the rostral aspect of the cerebellum.

Dentate gyrus - Medial aspect of the telencephalon. It caps the free edge of the hippocampus, which is part of the limbic system functioning in learning, memory and emotion.

Deep cerebellar nuclei - Lateral, interposital and fastigial nuclei are located in the cerebellar white matter, just dorsal to the fourth ventricle. They receive input from Purkinje neurons and also afferent fibres to the cerebellum (climbing and mossy); efferent fibres project to extrapyramidal upper motor neurons.

Deep mesencephalic nucleus - Lateral midbrain substance, located between the rostral colliculus, the substantia nigra and the periaqueductal gray. It is probably involved in nociception and visceral control.

Diagonal band - Bundle of cholinergic nerve fibres in the ventral, rostral cerebrum connecting the septal area with the hippocampus and lateral olfactory area.

Dorsal cochlear nucleus - Lateral, rostral medulla oblongata. See Cochlear nuclei.

Dorsal funiculus - Dorsal white matter of the spinal cord, medial to the dorsal horns. Main tracts are the funiculus gracilis and cuneatus. It principally consists of primary afferent projection neurons to nuclei in the brainstem involved in conscious proprioception.

Dorsal horn of the spinal cord - Grey matter in the dorsal spinal cord categorised variously into nuclei and laminae. It receives afferent information from the body and limbs, including impulse generated by tactile, proprioceptive nociceptive and interoceptive stimuli.

Dorsal median septum of the spinal cord - Longitudinal sheet of glial tissue in the median plane of the spinal cord that partitions the dorsal part of the spinal cord into right and left halves.

Dorsal median sulcus of the spinal cord - Shallow longitudinal groove in the dorsal midline of the spinal cord.

Dorsal nucleus of the lateral lemniscus - Prominent mass of grey matter dorsal to the trapezoid body in the rostral medulla oblongata. It receives afferent fibres from the cochlear nuclei (audition) and projects to the caudal colliculus via the lateral lemniscus.

Dorsal paraflocculus of cerebellum - see Paraflocculus.

Dorsal root - Afferent root of a spinal nerve. They convey sensory information, and there is one pair per spinal cord segment. At the distal end of the dorsal root is the spinal ganglion, which contains the neuronal somata of the nerve fibres conveyed by the root.

Dorsal spinocerebellar tract - White matter tract at the periphery of the dorsolateral spinal cord. It transmits subconscious proprioceptive information from spinal nerves caudal to the thoracic limb, via the caudal and rostral cerebellar peduncles to the ipsilateral cerebellar cortex.

Ectomarginal sulcus - Sulcus lateral to the similarly named gyrus on the dorsocaudal aspect of the brain. The caudal third of the ectomarginal gyrus extends into the occipital lobe.

Ectosylvian gyrus - Curved gyrus on the lateral side of the brain, principally in the temporal cortex.

Ectosylvian sulcus - Curved sulcus on the lateral side of the brain making up the ventral border of the ectosylvian gyrus.

Endomarginal gyrus - Gyrus bordering the longitudinal fissure on the dorsal aspect of the cerebrum.

Endomarginal sulcus - Lateral margin of the endomarginal gyrus.

Ent(d)opeduncular nucleus - Relatively large grey matter area in the ventral diencephalon (subthalamus), between the optic tract ventrally and the internal capsule dorsolaterally. It connects between the globus pallidus and the dorsal thalamus.

Endorhinal suclus - Ventral aspect of the olfactory peduncle of the telencephalon. It separates the olfactory tubercle from the lateral olfactory tract.

External capsule - Ventrolateral telencephalon, white matter tract separating the the lentiform nuclei and the claustrum. It connects motor areas of the telencephalon with the basal nuclei.

Extreme capsule - Ventrolateral telencephalon, white matter tract separating the claustrum from the cortex of the temporal lobe.

Facial nerve - Cranial nerve VII, the nucleus is located in the ventral, rostral medulla oblongata. Its principal function is innervation of muscles of facial expression but it also sends efferent fibres to the stapedius muscle of the inner ear, and parasympathetic fibres to palatine and lacrimal salivary glands. Afferent fibres convey taste from the rostral two-thirds of the tongue.

Fasciculus cuneatus - Large white matter tract in dorsal funiculus of the spinal cord, lateral to fasciculus gracilis. It comprises axons from primary afferent neurons from the body and limbs, which enter the fasciculus without synapsing in the dorsal horn. They convey conscious proprioceptive information from the neck, thoracic limbs, and cranial half of the trunk to the medial cuneate nucleus in the caudal medulla oblongata. Fibres that enter the caudal portion of the tract are located medially.

Fasciculus gracilis - Medially located tract in the dorsal funiculus of the spinal cord. It is organised like the fasciculus gracilis and conveys the same type of information but from the caudal trunk and pelvic limbs to the nucleus gracilis in the caudal medulla oblongata.

Fastigial nucleus of cerebellum - The most medial of the three, paired cerebellar nuclei in the deep white matter of the cerebellum. It receives input from the vermis and its efferent fibres project to the vestibular and reticular nuclei of the brainstem.

Fimbria - Medial aspect of the caudal telencephalon, extending along the lateral edge of the hippocampus. It comprises myelinated axons originating from the hippocampus and continues rostrally as the fornix.

Flocculus of cerebellum - Small lobule of the ventrolatereral cerebellum at the caudal border of the middle

cerebellar peduncle. It is part of the vestibulocerebellum.

Folia of cerebellum - Folds of cerebellar cortex (gyrus).

Fornix of the hippocampus - Medial aspect of the cerebral hemispheres, ventral to the corpus callosum. It comprises the efferent white matter of the hippocampus continuing rostrally and consists of crura, body and columns. It connects to the opposite side by commissural fibres.

Fourth ventricle - The most caudal of the four, connected, fluid-filled cavities within the brain. It extends from the mesencephalic aqueduct to the obex in the caudal medulla oblongata, and is filled with cerebrospinal fluid.

Frontal gyrus - Most rostral gyrus on the medial side of the frontal lobe of the telencephalon. It is dorsal to the straight gyrus and olfactory bulb.

Genual gyrus - Gyrus rostral to the genu of the corpus callosum, medial aspect of the rostral telencephalon.

Genual sulcus - Caudal margin of the genual gyrus.

Globus pallidus - Ventral to the lateral ventricle of the telencephalon, it is the ventral nucleus of the lentiform nuclei and a component of the basal nuclei. It facilitates activity in extrapyramidal nuclei.

Habenular nuclei (medial and lateral) - Part of the epithalamus of the diencephalon, situated on the dorsomedial surface of the thalamus. They are involved in many functions, including pain processing, behavioural and stress responses, and learning.

Habenulointerpeduncular tract (fasciculus retroflexus) - Dorsomedial thalamus. This is a compact bundle of fibres arising in the habenula nuclei and passing ventrally to the interpeduncular nucleus at the base of the midbrain. This primitive tract carries negative feedback from forebrain caudally onto midbrain reward cells. In humans, drug abuse specifically results in degeneration of fibres in this tract.

Hippocampus - Paleontologically ancient, internal gyrus of the telencephalon, forming the medial wall and roof of the caudal half of the lateral ventricle. It arches dorsally, medially and rostrally. Afferent and efferent axons of the hippocampus form the alveolus and combine to form the fimbria continuing rostrally as the fornix of the hippocampus. It is part of the limbic system and is associated with emotion, learning and memory. The hippocampal formation comprises the hippocampus proper, the subiculum and the dentate gyrus.

Hypoglossal nerve roots - CN XII axons arising from the hypoglossal nucleus that course ventrolaterally through the caudal medulla oblongata to form the cranial nerve supplying tongue muscles.

Hypoglossal nucleus - Nucleus of CN XII in the dorsal, caudal medulla oblongata, ventromedial to the parasympathetic nucleus of CN X.

Infundibular recess - Ventral extension of the third ventricle of the diencephalon. It forms a funnel-shaped recess extending into the infundibulum.

Infundibulum - A funnel-shaped, ventral extension of the hypothalamus connecting the caudal pituitary gland with the hypothalamus.

Intermediate olfactory stria - See Olfactory tract.

Internal arcuate fibres - Efferent fibres arising from the gracile and medial cuneate nuclei of the caudal, dorsal medulla oblongata. These fibers decussate to form the medial lemniscus and convey sensory information from the body and limbs to the thalamus and then onto the somatosensory cortex.

Internal capsule - Prominent white matter tract ventrolateral to the lateral ventricles of the telencephalon that connect bidirectionally between the brainstem and the cerebral cortex.

Interpeduncular nucleus - An unpaired, ovoid cell group lying between the cerebral peduncles on the ventral aspect of the midbrain. It receives information from the habenula nuclei and projects to the raphe nuclei and periaqueductal gray substance of the midbrain. It may have a role in the regulation of rapid eye movement sleep.

Interposital nucleus - Middle of the three, deep cerebellar nuclei in the white matter of the cerebellum. It receives fibres from the paravermal cerebellar cortex and its efferent fibres exit via the rostral cerebellar peduncle to connect with contralateral brainstem nuclei.

Interthalamic adhesion - Flattened band of grey matter connecting the medial walls of the left and right thalami. It contains neurons and axons, but very few appear to cross the mid-line, and humans lacking this structure appear to suffer no consequences.

Interventricular foramen - Channels that connect the paired lateral ventricles of the telencephalon with the third ventricle on the midline of the diencephalon. Cerebrospinal fluid produced in the lateral ventricles connects via the foramens to the third ventricle. Choroid plexus from the lateral ventricles protrudes through this foramen and is continuous with that of the third ventricle.

Lateral aperture - Opening of the fourth ventricle at the level of the cerebellar peduncles, allowing CSF to flow into the subarachnoid space. In non-primates, this is the only brain connection between the ventricular system and the subarachnoid space.

Lateral cuneate nucleus - Lateral to the medial cuneate nucleus on the dorsal aspect of the caudal medulla oblongata. It receives proprioceptive information from muscle spindles and Golgi tendon organs receptors from the cranial half of the body and thoracic limbs. Axons from the lateral cuneate nucleus enter the adjacent caudal cerebellar peduncle and pass into the cerebellum (subconscious proprioception).

Lateral funiculus - Large region of white matter in spinal cord located laterally and bounded by the dorsal and ventral roots. It contains ascending sensory and descending motor tracts, specifically those that influence flexor muscle activity.

Lateral geniculate nucleus - Dorsolateral aspect of the caudal diencephalon (metathalamus), caudal to the thalamus. It is part of the visual pathway.

Lateral lemniscus - White matter tract of the auditory system, in the brainstem, extending from the cochlear nuclei and trapezoid body to the caudal colliculi of the midbrain.

Lateral nucleus of the cerebellum - The most lateral of the three deep cerebellar nuclei in the white matter of the cerebellum. It receives fibres from the cerebellar hemisphere and its efferent fibres exit via the rostral cerebellar peduncle to connect with contralateral brainstem nuclei.

Lateral olfactory stria - See Olfactory tract.

Lateral reticular nucleus - See Reticular nuclei.

Lateral rhinal sulcus - Dorsal margin of the rhinencephalon, located on the ventrolateral aspect of the cerebrum.

Lateral septal nucleus - see Septal nuclei.

Lateral ventricle - Fluid-filled cavity oriented longitudinally in each cerebral hemisphere. It is the most rostral part of the ventricular system.

Lateral vestibular nucleus - Medial to the caudal cerebellar peduncle in the medulla oblongata. See Vestibular nuclei.

Lentiform nuclei - Putamen plus globus pallidus; a component of basal nuclei.

Lingula - see Cerebellar vermis.

Longitudinal fibres of the pons - Contains axons projecting from the cerebral cortex, via the internal capsule and crus cerebri. Some longitudinal fibres synapse on pontine nuclei and proceed to the cerebellum, while others pass to other brainstem nuclei (corticonuclear tract) or via the pyramids to the spinal cord (corticospinal tract).

Longitudinal fissure - Fissure separating the two hemispheres of the vertebrate brain.

Mammillary body - Caudal and ventral hypothalamus, forming bulges on the ventral aspect of the forebrain. It has links with the hippocampus (via the fornix), the thalamus and midbrain tegmentum. The mammillary nuclei are associated with the limbic system.

Mammillothalamic fasciculus - Connects the mammillary body to the midbrain tegmental nuclei and to the rostral thalamic nucleus.

Marginal gyrus - Gyrus lateral to the endomarginal gyrus on the dorsal aspect of the cerebrum.

Marginal sulcus - Lateral border of the marginal gyrus.

Medial cuneate nucleus - Nucleus on the dorsal aspect of the caudal medulla oblongata. It receives information from specialised touch, pressure, vibration and joint receptors from the thoracic limbs and cranial trunk. Efferent axons from this nucleus decussate in the internal arcuate fibres and travel rostrally as part of the medial lemniscus to the thalamus and somatosensory cortex (conscious proprioception).

Medial geniculate nucleus - Lateral aspect of the caudal diencephalon caudal to the thalamus, a component of the metathalamus. It is part of the auditory pathway.

Medial lemniscus - Sensory pathway travelling rostrally through the substance of the brainstem to the thalamus. It conveys the majority of information from the mechanoreceptors that mediate tactile discrimination and proprioception, from the nucleus gracilis and medial cuneate nuclei to the thalamus. Fibres arising from the trigeminal nuclear complex (which receives sensory input from the head) also travel with it (quintatothalamic tract).

Medial longitudinal fasciculus - Median brainstem, ventral to the ventricular system. It conveys fibres rostrally from the vestibular nuclei to synapse on the motor nuclei of cranial nerves III, IV and VI; this connection functions in the vestibulo-ocular reflex. This fasciculus also projects to the reticular formation (basis of motion sickness) and extends caudally into the spinal cord reaching cranial thoracic level; this part of the fasciculus is involved in maintaining head position.

Medial olfactory stria - see Olfactory tract.

Medial rhinal sulcus - Ventromedial aspect of the rostral telencephalon. It forms the medial boundary of the olfactory peduncle and meets with the rostral aspect of the lateral rhinal sulcus dorsal to the peduncle, thereby separating the peduncle from the frontal cortex.

Medial septal nucleus - see Septal nuclei.

Medial vestibular nucleus - Medial to the caudal cerebellar peduncle in the medulla oblongata. See Vestibular nuclei.

Mesencephalic aqueduct - Portion of the ventricular system reduced to a small tube extending through the midbrain. It connects the third and fourth ventricle.

Mesencephalic nucleus of V - Thin column of large neurons on the lateral border of the central grey matter of the mesencephalon. Afferent fibres are proprioceptive from the mouth, including the teeth, and muscles of mastication. Their cell bodies are located in this nucleus, hence the nucleus is the equivalent of a ganglion. Efferent fibres project to the motor nucleus of V (mastication) or via the medial lemniscus to the thalamus and somatosensory cortex for conscious perception. The nucleus is absent in lampreys and hagfishes (the only vertebrates without jaws).

Mesencephalic tract of V - Narrow tract on the periphery of the mesencephalic nucleus of V. It contains axons travelling between the trigeminal nerve and the nucleus.

Middle cerebellar peduncle - Neuronal processes on each side of the fourth ventricle connecting the transverse fibres of the pons with the cerebellum. It conveys afferent fibres only, from the pons (part of the corticopontocerebellar pathway).

Motor nerve roots - Efferent fibres within the brainstem or spinal cord travelling towards the peripheral nervous system.

Myelencephalon - Medulla oblongata.

Nodulus - see Cerebellar vermis. This ventrocaudal portion of the vermis is associated with the vestibulocerebellum.

Nucleus accumbens - Rostro-ventral telencephalon, located between the head of the caudate nucleus and the septal nuclei. It is a ventral extension of the caudate nucleus, which is a component of the basal nuclei.

Nucleus ambiguus - Poorly defined, elongated nucleus in the ventrolateral substance of the caudal medulla oblongata. Efferent fibres form the glossopharyngeal (CN IX), vagus (CN X) and the cranial roots of accessory nerve (CN XI), to innervate the striated muscle of the pharynx, larynx and oesophagus.

Nucleus gracilis - Nucleus on the dorsal aspect of the caudal medulla oblongata, medial to the medial cuneate nucleus. It receives proprioceptive information from specialised touch, pressure, vibration and joint receptors from the pelvic limbs and caudal trunk. Axons from neurons in the nucleus gracilis decussate in the internal arcuate fibres and travel rostrally as part of the medial lemniscus to the thalamus and somatosensory cortex.

Nucleus of the solitary tract - Nucleus dorsal to the sulcus limitans of the fourth ventricle in the caudal medulla oblongata. It receives afferent fibres carrying visceral sensation and taste from the facial (VII),

glossopharyngeal (IX) and vagus (X) cranial nerves.

Nucleus of the spinal tract of V - Prominent sensory nucleus located in the dorsal brainstem extending from the pons to the cranial cervical spinal cord. It receives input from the trigeminal, facial, glossopharyngeal and vagus nerves especially associated with noxious and thermal stimuli. It is continuous with the substantia gelatinosa of the spinal cord. Efferent fibres are involved in reflex cranial nerve activity and project to the somatosensory cortex.

Occipital gyrus - Most caudal gyrus of the occipital lobe, caudal telencephalon.

Occipital pole - Caudal portion of the occipital lobe, caudal telencephalon.

Oculomotor nerve - CN III, exits the ventral aspect of the caudal midbrain. It conveys somatic motor fibres to the majority of the extraocular muscles (ventral, medial, and dorsal rectus and ventral oblique muscles), as well as parasympathetic fibres to the ciliary ganglion and smooth muscles of eye and orbit. It is the efferent arm of the pupillary light reflex.

Oculomotor nerve roots - CN III axons within the parenchyma of the midbrain tegmentum.

Oculomotor nucleus - Nucleus of CN III in the midbrain, ventral to the mesencephalic aqueduct. It comprises somatic motor neurons that innervate the striated, extraocular muscles. Just dorsal to this nucleus is the separate parasympathetic nucleus of III; fibres from this nucleus innervate the smooth muscle of the pupillary constrictor and the orbit.

Olfactory bulb - Ventral and most rostral part of the telencephalon, expanded rostral aspect of the olfactory peduncle. Olfactory bulb neurons receive input from olfactory cells in the olfactory epithelium, and project via the olfactory tract (see Olfactory tract).

Olfactory nucleus - Grey matter in the olfactory peduncle, ventro-rostral telencephalon. It is one of the relay stations in the olfactory pathway from the olfactory bulb to the piriform lobe.

Olfactory peduncle - Longitudinal bulge on the ventral and rostral aspect of the telencephalon extending from the olfactory bulb to the olfactory tubercle. The peripheral grey matter layer is the olfactory nucleus and the central white matter is the olfactory tract.

Olfactory tract - The tract conveys axons from neurons in the olfactory bulb. It divides into the medial, intermediate and lateral olfactory stria. The lateral olfactory stria axons synapse in the olfactory tubercle and then continue to the primary olfactory cortex in the piriform lobe. Fibres in the intermediate olfactory stria decussate via the rostral commissure and project to the contralateral olfactory bulb. Fibres from the medial olfactory tract connect to the septal nuclei and from there, via the medial forebrain bundle, to the hypothalamus or reticular formation for olfacto-visceral reflexes. Note: the terms ‘olfactory tract’ and ‘olfactory stria’ seem to be used somewhat interchangeably.

Olfactory tubercle - Ventral and rostral forebrain, forms a bulge at the caudal end of the olfactory peduncle. It is one of the relay stations in the olfactory pathway from the olfactory bulb to the piriform lobe.

Olivary nucleus - Prominent nuclear complex within the ventrocaudal medulla oblongata on the dorsolateral border of the pyramids. Afferent fibres are mostly from the extrapyramidal motor system and the cerebellum. Efferent fibres form the climbing fibres that decussate and ascend into the contralateral cerebellum via the caudal cerebellar peduncle.

Optic chiasm - Single structure rostral to the infundibulum on the ventro-rostral aspect of the forebrain. It is the site of attachment of the optic nerves, part of the visual pathway and where the majority of optic nerve fibres decussate.

Optic nerve - CN II originating in the optic retina conveys axons from retinal ganglion cells to the brain. Although it is a cranial nerve, it is an extension of the CNS as it is myelinated by oligodendroglia. The left and right optic nerves join at the optic chiasm ventral to the hypothalamus.

Optic tract - Part of the diencephalon, continuation of retinal ganglion cell axons caudal to the optic chiasm. The tract projects caudally and dorsally to the lateral geniculate nucleus of the thalamus and to the midbrain.

Paraflocculus of cerebellum - Lobule on the ventrolateral aspect of the cerebellar hemisphere. It has dorsal and ventral components.

Parahippocampal gyrus - Cerebrocortical gyrus on the ventromedial surface of the temporal lobe, bordering the hippocampus; it is continued dorsally by the cingulate gyrus. It connects to the hippocampus proper by the subiculum.

Paramedian lobule of cerebellum - Lobule lateral to caudal portion of cerebellar vermis.

Parasympathetic nucleus of X - Nuclear column in the caudal medulla oblongata, dorsolateral to the hypoglossal nucleus, and lateral to the sulcus limitans of the fourth ventricle. Efferent axons form the vagus nerve that provides parasympathetic innervation to the thoracic and abdominal viscera.

Pineal gland - Small endocrine gland that projects caudally from the dorsal aspect of the third ventricle, on the midline between the cerebral hemispheres. It produces serotonin and its derivative melatonin, a hormone that modulates wake/sleep patterns and seasonal functions.

Piriform lobe - Cerebral cortex on the caudal part of the ventrolateral aspect of the telencephalon. It is the primary receiving area for olfactory stimuli and is part of the rhinencephalon involved in olfaction.

Pons (metencephalon) - Portion of the brainstem between the midbrain and medulla oblongata. Important components include the motor nucleus of the trigeminal nerve (CN V), the transverse fibres of the pons, pontine nuclei and the nucleus of the trapezoid body.

Pontine nucleus - Scattered nuclei in the ventral pons. Afferent fibres are from the cerebral cortex. Efferent fibres form the transverse fibres of the pons, which decussate and ascend via the contralateral middle cerebellar peduncle to the cerebellum; it is part of the corticopontocerebellar pathway.

Pontine raphe - Nucleus consisting of a small number of serotonergic neurons in the midline of the pons; it also extends into the medulla oblongata.

Pontine reticular nuclei - Diffuse network of neurons in the substance of the pons. They are important in regulating consciousness or wakefulness. See Reticular nuclei.

Postcruciate gyrus - Gyrus on dorsal surface of the rostral cerebrum, immediately caudal to the cruciate sulcus. It is part of the motor cortex.

Presylvian sulcus - Sulcus on the rostrolateral aspect of the cerebrum rostral to the pseudosylvian fissure. It forms the border between the lateral rostral composite gyrus and the more rostral prorean gyrus.

Primary fissure of cerebellum - Transverse sulcus on the dorsal cerebellum. It separates the body of the cerebellum into rostral and caudal lobes.

Prorean gyrus - Rostral gyrus on the ventrolateral aspect of the rostral telencephalon rostral to the presylvian sulcus and dorsolateral to the olfactory peduncle.

Pseudosylvian fissure - Lateral aspect of the telencephlon, in the temporal lobe. The primary auditory cortex is situated around this fissure.

Putamen - Component of the basal nuclei, lateral to the internal capsule in the substance of the rostral telencephalon. It, and the globus pallidus, comprise the lentiform nuclei.

Pyramid - Prominent longitudinal bulge on the ventral surface of the caudal, medial medulla oblongata. It comprises caudally directed corticospinal fibres, which facilitate voluntary motor function especially of skilled activities.

Pyramidal decussation - Ventrocaudal medulla oblongata at the spinomedullary junction. It is the site where the pyramids become less prominent as they cross to the contralateral side and a more dorsolateral position in the spinal cord.

Pyramis - see Cerebellar vermis.

Red nucleus - Prominent upper motor neuron nucleus in tegmentum of midbrain, ventrolateral to the oculomotor nucleus. It is named such because of its rich vascularisation. Afferent fibres are from the lateral (dentate) nucleus of the cerebellum, which are projected onto the thalamus (dentatorubrothalamic pathway) as a major feedback route to the cerebrum from the cerebellum. Efferent fibres decussate immediately and project to brainstem nuclei (CNN V, VII, IX-XI) and to the spinal cord. It is involved in semi-automatic movements such as swallowing, chewing and sucking, and flexor activities such as sitting.

Reticular nuclei - Form a complex, poorly defined network extending through the core of the brainstem. It includes the gigantocellular and parvocellular nuclei (medulla oblongata). The lateral area receives afferent fibres from the spinal cord, cerebellum and forebrain. Efferent fibres arise from the medial area and have diverse functions including modulating respiration, heart rate and blood pressure, protective reflexes (coughing and vomiting) and maintenance of consciousness via connections to the cerebrum (ascending reticular activating system). It is involved in regulating rhythmical activities, and is also the origin of the reticulospinal tracts; different reticulospinal tracts stimulate, or inhibit, motor activity of the body and limbs.

Rostral cerebellar peduncle - Connects the cerebellum with the midbrain. It contains mainly efferent processes from the interposital and lateral cerebellar nuclei exiting the cerebellum and travelling to contralateral brainstem nuclei. It also conveys afferent fibres from the craniospinocerebellar, ventral spinocerebellar and rubrocerebellar tracts.

Rostral colliculus - Prominent dorsal protuberance on the tectum of the midbrain. It functions as a reflex centre for visual pathways receiving afferent fibres from the optic tract, visual cortex, caudal colliculus and spinal cord (spinomesencephalic tract). Efferent fibres (tectobulbar and tectospinal) influence movement of the eyes, ears and head in response to visual and auditory stimuli.

Rostral commissure - Small commissure in the rostral, ventral telencephalic substance around which the

columns of the fornix split. The commissure connects the olfactory bulbs on each side.

Rostral lobe of cerebellum - Separated from caudal lobe by the dorsally located, transverse, primary fissure. It is especially inhibitory to extensor muscles.

Rostral rhinal sulcus - Rostral extension of lateral rhinal sulcus making up the dorsal margin of the olfactory peduncle.

Rostral suprasylvian gyrus - Rostral extent of the suprasylvian gyrus on the lateral aspect of the rostral cerebrum.

Rostral vestibular nucleus - Pons, at the level of the rostral cerebellar peduncle. See vestibular nuclei.

Rubrospinal tract - UMN axons extending from the red nucleus of the midbrain tegmentum, caudally through the brainstem into the lateral funiculus of the spinal cord, medial to the dorsal spinocerebellar tract. It is important in facilitating flexor motor function for voluntary and postural activities.

Sensory roots of the trigeminal nerve - Pontine-medullary junction. Axons coursing dorsomedially from the trigeminal nerve to the sensory nucleus of the trigeminal nerve.

Septal nuclei (medial and lateral) - Located rostral to the rostral commissure on the medial aspect of the rostral telencephalon. They form the medial wall of the rostral aspect of the lateral ventricle, and attach dorsally to the corpus callosum. It receives input from the medial olfactory stria and has reciprocal connections with the hippocampus and hypothalamus. The septal nuclei, along with the nucleus accumbens, play a role in reward and reinforcement.

Septum pellucidum - A midline, fibrous lamina that connects between the septal nuclei and the corpus callosum, separating the rostral aspect of the lateral ventricles.

Solitary tract - Dorsolateral medulla oblongata, ventral to the floor of the fourth ventricle. It conveys afferent fibres carrying visceral sensation and taste from the facial (VII), glossopharyngeal (IX) and vagus (X) cranial nerves to the adjacent solitary nucleus.

Solitary tract nucleus - see Nucleus of the solitary tract.

Spinal nerve - Nerves emerging from the spinal cord. Each spinal nerve comprises dorsal and ventral roots. These are mixed nerves conveying sensory, motor and, in the thoracolumbar and sacral regions, autonomic fibres.

Spinal tract of V - Tract in the dorsolateral pons and medulla oblongata, dorsolateral to its nucleus. It conveys primary visceral afferent axons from ganglia of CNN V, VII, IX and X.

Splenial gyrus - Gyrus on the caudal aspect of the medial cerebral hemispheres. It is bordered by splenial sulcus ventrally and the supraspenial sulcus dorsally.

Splenial sulcus - Rostral border of the splenial gyrus on caudal and medial aspect of the cerebral hemispheres.

Straight gyrus - Rostral telencephalon, the gyrus on the ventral aspect of the longitudinal fissure. It is medial to the olfactory peduncle and the lateral ventricle.

Stria terminalis - Medial cerebrum, in the angle between the thalamus and the caudate nucleus. It conveys efferent fibres from the amygdala (basal nuclei) to the rostral hypothalamus. The amygdala influences behaviour, autonomic activity and movement.

Subarachnoid space - CSF-filled space between the arachnoid mater and pia mater surrounding the CNS. It is criss-crossed by fine arachnoid trabeculae. On the lateral aspect of the spinal cord, the space is traversed by paired denticulate ligaments, formed from thickenings of the pia mater and which attach the spinal cord to the spinal dura mater. The subarachnoid space collapses at death due to lack of CSF pressure.

Subcallosal fasciculus - Bundle of nerve fibres running longitudinally in the dorsolateral aspect of lateral ventricles of the cerebral hemisphere, beneath the lateral angle of the corpus callosum. It has similar connections to the cingulate gyrus (part of the limbic system) and also connects to the caudate nucleus.

Substantia nigra - Longitudinal nuclei, producing dopamine, on the ventral aspect of the mesencephalon, dorsal to the crus cerebri. It may be pigmented, especially in older animals. It is associated with the basal nuclei and the extrapyramidal motor system.

Sulcus limitans - Sulcus in the lateral wall of the spinal canal, fourth ventricle and mesencephalic aqueduct; it is only grossly visible in the fourth ventricle. Embryologically, it divided the neural tube into the dorsal/sensory alar plate and the ventral/motor basal plate.

Supracollosal gyrus - Small gyrus sited dorsal to the rostral corpus callosum on the medial side of the cerebrum. It is part of the small, supracallosal portion of the hippocampal formation.

Supraspenial sulcus - Sulcus forming the rostral margin of the occipital gyrus on the caudomedial border of the cerebrum.

Suprasylvian gyrus - Elongated, curving gyrus on lateral aspect of the cerebrum. It is bounded ventrally by the suprasylvian sulcus and dorsally by the marginal sulcus.

Suprasylvian sulcus - Ventral to the suprasylvian gyrus on the lateral side of the cerebrum.

Sylvian gyrus - Gyrus surrounding the pseudosylvian fissure on the lateral side of the cerebrum. It comprises the auditory cortex.

Tectum - Dorsal part of the midbrain. It is formed primarily by the paired rostral and caudal colliculi, which together, make up the corpora quadrigemina. It primarily functions in visual and auditory reflexes.

Tegmental fasciculus - Fibre bundle passing longitudinally through the central mesencephalic and pontine tegmentum, lateral to the medial longitudinal fasciculus. It contains fibres from the mesencephalic tegmentum and regions surrounding the central gray substance travelling caudally to the olivary nucleus; and fibres travelling rostrally from more caudal reticular formation to the diencephalon.

Tegmentum - Ventral part of the midbrain. It includes the oculomotor and red nuclei as well as the substantia nigra and crus cerebri.

Thalamic nuclei - Part of the diencephalon on the medial aspect of the forebrain. The thalamic nuclear group comprises numerous nuclei that are divided into major groups by medullary lamina. The thalamic nuclei act as a relay between a variety of subcortical areas and the cerebral cortex and form numerous bidirectional links with the cerebral cortex.

Third ventricle - CSF-filled, ring-shaped cavity, vertically oriented around the interthalamic adhesion of the diencephalon; part of the ventricular system.

Transverse fibres of the pons - Prominent fibres on the ventral aspect of the pons. They consist of axons arising from the pontine nuclei, which decussate and ascend into the cerebellum via the middle cerebellar peduncles.

Transverse fissure - Located between the caudal poles of the cerebrum and the rostral face of the cerebellum. It contains the fibrous tentorium cerebelli, an extension of the dura mater, which arises from the osseous tentorium.

Trapezoid body - Large band of transverse fibres on the ventral surface of the rostral medulla oblongata. It is formed by fibres of the ventral cochlear nucleus and is part of the pathway projecting auditory stimuli rostrally.

Trochlear nucleus - Nucleus of the fourth cranial nerve, situated in the midbrain tegmentum caudal to the oculomotor nuclei. Uniquely, its fibres exit the brainstem dorsally and decussate. They innervate the dorsal oblique, extraocular muscles.

Tuber - See Cerebellar vermis.

Uvula of cerebellum - See Cerebellar vermis.

Uvulonodular fissure of cerebellum - Ventrocaudal aspect of the cerebellum, separates the large body of the cerebellum from the small flocculonodular lobe.

Ventral cochlear nucleus - Lateral aspect of the rostral medulla. See Cochlear nuclei.

Ventral funiculus - Ventral region of white matter of the spinal cord between the ventral median fissure and the ventral root. Principally consists of caudally directed, upper motor neuron tracts that facilitate extensor muscle function.

Ventral horn of the spinal cord - Ventral grey matter of the spinal cord, contains somata of lower motor neurons supplying the neck, trunk and limbs.

Ventral median fissure - Longitudinal groove in the midline of the ventral aspect of the spinal cord and the medulla oblongata.

Ventral paraflocculus of cerebellum - see Paraflocculus of the cerebellum.

Ventral reticular nucleus - see Reticular nuclei.

Ventral spinal root - Efferent/motor root of a spinal nerve. See Spinal nerve.

Ventral spinocerebellar tract - Tract conveying subconscious proprioceptive fibres from the caudal half of the body to the cerebellum via the rostral cerebellar peduncle. The tract decussates in the spinal cord and then again in the cerebellum.

Vestibular nuclei - Four pairs (rostral, medial, lateral and caudal) located in the dorsal aspect of the rostral medulla oblongata around the cerebellar peduncles, adjacent to the lateral aspect of the fourth ventricle. They receive input from the vestibular nerve (head proprioception), the cerebellum and the spinal cord. Their axons project to the cerebellum (subconscious proprioception), the somatosensory cortex (conscious proprioception), motor nuclei of the extraocular muscles (head and eyeball position - vestibulo-ocular reflex), the spinal cord (postural adjustments to accommodate changes in head position) and the reticular formation (basis of motion sickness).

Vestibulocochlear nerve - CN VIII, attaches to the brainstem laterally at the pontine-medullary junction. It

conveys afferent axons from vestibular and cochlear receptors in the inner ear.