THE SPLEEN
A general impression of the visceral topography should be obtained from Figure 28-4 before the individual organs are considered.
The flat oblong spleen is situated over the craniodor- sal part of the rumen, against the left half of the diaphragm, and is attached to both these organs.
Its upper end lies under the dorsal ends of the last few ribs, and its axis extends ventrally, with a slight cranial inclination, across the line of the ribs to end in the region of the seventh costochondral joint (Figure 28-4, AJ2 and Figure 28-5/6). In most animals the lower end passes onto the reticulum, which brings risk of involvement in the common abscesses and perforations of that organ. The upper part of the spleen is retroperitoneal: the line of serosal reflection runs cranioventrally over both parietal and visceral surfaces. The hilus is confined to the dorsocranial angle of the medial side, and to reach this site, the splenic vessels must first pass over the roof of the rumen.The capsule contains little muscle, and physiological variation in spleen size is therefore rather restricted. Occasionally an enlarged spleen may extend behind the last rib in the angle between this and the lumbar spine, but for practical purposes the spleen may be regarded as out of reach for palpation or percussion. Access for a biopsy is normally made through the upper end of the eleventh intercostal space and involves little risk of injury to the lung, particularly if the needle is introduced during expiration.
The spleen has a relatively soft consistency. Its color varies considerably, tending to be steel blue in cows and more reddish in males and younger animals. The division of the pulp into red and white areas is very obvious; the white corpuscles are somewhat larger than pinheads.
The spleen is relatively small in sheep and goats, in which its form, position, and attachments resemble those of the dorsal extremity of the bovine organ. It is roughly triangular in sheep and quadrilateral in goats (Figure 28-6, B-C).