» Conformation and Surface Anatomy
The form of the abdomen varies with age, obesity, and physiologic 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 steepness is not obvious on first inspection because the caudal part of the abdomen is covered by the thighs and the skinfolds 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 (see Fig. 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 (Table 28.1). The upper part of the flank is dished, forming the paralumbar fossa beside the loins (see Fig. 26.1/S and 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 Fig. 26.1A). Not all of these are palpable, although identification of the margin of the thoracic cage, the coxal tuber, and most lumbar transverse processes normally presents no problem. The correct identification of the bones with palpation is important in certain anesthetic techniques. Out of the six lumbar vertebrae in cattle, the second to fifth vertebrae are easy to recognize and may even be identifiable without palpation in lean cattle. The first process, however, 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 Fig. 26.5). There are occasionally seven lumbar vertebrae in sheep and goats.