CONFORMATION AND SURFACE ANATOMY THE VENTROLATERAL WALL OF THE ABDOMEN
The form of the abdomen varies with age, obesity, and physiological condition. In adult animals it is both deep and wide, and the floor, which dips behind the sternum, ascends very steeply in its caudal part to join the pubic brim.
This marked contraction is not obvious on first inspection because the caudal part of the abdomen is covered by the thighs and the skin folds that pass between the flanks and stifle joints and is overlain ventrally by the udder or the prepuce. The considerable extent of the abdomen under cover of the ribs follows from the curvature of the diaphragm (Figure 27-3). The abdomen is usually bilaterally symmetrical, although advanced pregnancy or excessive distention of the rumen may cause one side to bulge more markedly. The upper part of the flank is dished, forming the paralum- bar fossa beside the loins (see Figure 26-1, B, E), while the lower convex part merges with the floor.In the younger calf the abdomen is shallower and laterally compressed, and the floor slopes more gradually to the pelvis; the spreading of the caudal ribs, the deepening of the trunk, and the depressions beside the vertebral column develop with growth of the rumen.
The lateral and ventral abdominal walls are bounded by the last rib and costal arch, the extremities of the lumbar transverse processes, the coxal tuber, and the terminal line of the pelvic inlet (see Figure 26-1, A). Not all of these are palpable, although identification of the margin of the thoracic cage, the coxal tuber, and most transverse processes normally presents no problem. Palpation should be performed with care because correct identification of the bones is important in certain anesthetic techniques. There are six lumbar vertebrae in cattle. Recognition of the second to fifth vertebrae is easy and may even be possible without palpation in lean cattle; the first process cannot always be located because it is short, tucked into the angle between the last rib and the spine, and generally overlain by a pad of fat; the last one always eludes the fingers because it lies medial to the coxal tuber below a thick covering of muscle (see Figure 26-5). There are occasionally seven lumbar vertebrae in sheep and goats.