CONFORMATION AND SURFACE FEATURES
The back and loins are shaped over the framework of the thoracic and lumbar vertebrae. The loins are sharply divided from the flanks by the prominent tips of the lumbar transverse processes, but the boundaries of the back cannot be defined so precisely because the back blends smoothly with the lateral thoracic wall and incorporates the upper line of the shoulder blades with their cartilages and covering muscles.
It is convenient to include in this chapter the few observations that are necessary on the dorsal sacral region, which merges with the quarters and root of the tail.In the animal standing quietly, the dorsal contour is slightly raised over the withers, but otherwise it follows a fairly straight line from immediately behind the skull to the tail root (Figure 26-1). The line of the neck, which is based on the funicular part of the nuchal ligament, varies of course with the carriage of the head.
The dorsal contour of the trunk is prescribed by the summits of the spinous processes of the vertebrae, many of which can be palpated separately. Identification of individual bones is most reliable if begun at the wide space between the upright process of the last lumbar vertebra and the sloping cranial margin of the median sacral crest. The sacral crest can be followed caudally until it is succeeded by the separate projections of the spinous processes of the caudal vertebrae; any doubt about the identity of these processes may be resolved by pumping the tail up and down to discover the very mobile joint between the first and second tail bones. Certainty in identifying the first intercaudal space has a special importance because this is the site for injection of local anesthetic when producing “low” epidural anesthesia (p. 667). The tail root is sometimes elevated, especially in cows during estrus.
Working cranially from the lumbosacral space, the lumbar spinous processes are easily distinguished in lean animals.
Enumeration becomes more difficult over the caudal part of the chest where several processes converge, and the count is completely lost where the vertebrae become enclosed between the scapular cartilages. The first thoracic spine lies cranial to the scapulae, where it can be felt on deep palpation even though it fails to approach close to the skin. The cervical vertebrae cannot be reached from above, but their general position is detectable on palpation from the side. The transverse processes are well developed and divided into two parts, of which the ventral one is quite large; this is very obvious at the sixth cervical vertebra. Despite this, the individual identification of these bones is difficult until the wing of the atlas provides an unmistakable landmark.Additional features that may be picked out in the region of the hindquarters include the salient sacral tubers of the pelvis, which lie to each side of the lumbosacral space, and the strong iliac crests, which join these projections to the coxal tubers. The crests are raised above their surroundings and are crossed by cranial prolongations of the gluteal musculature.
The head is carried higher in sheep and goats; these species also slope at the croup (Figure 26-2).