THE BRAIN AND SPINAL CORD
The brain is small, indeed, barely larger than one of the eyes (Figure 37-38). The cerebral hemispheres are pearshaped; their pointed rostral ends (olfactory bulbs) are wedged between the large orbits.
Compared with their mammalian counterparts, the hemispheres are small and relatively smooth. The right and left hemispheres are separated from each other by a median fissure and from the cerebellum by a transverse fissure. The tip of the epiphysis can be seen at the intersection of those fissures. The optic lobes, homologous with the rostral colliculi of the mammal, are located caudoventral to the hemispheres. They are exceedingly large—corresponding to the development of the eyes—and are visible from both dorsal and ventral aspects. The optic chiasm (Figure 37-38/6) is also correspondingly large. (The small olfactory bulbs point to an underdeveloped sense of smell.) The cerebellum (Figure 37-38/12), also relatively large, consists essentially of a central body (the homologue of the mammalian vermis) with small lateral appendages (flocculi).A peculiarity of the spinal cord is a glycogen-rich gelatinous body at the dorsal surface of the lumbosacral enlargement; it is 3 to 5 mm in size and should not be mistaken for a lesion.
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