50 



Anatomy of the Rabbit. 



is divided into three chief portions — the pulmonary pleura, investing the 

 greater part of each organ, the costal pleura, lining the internal surface of 

 the thorax, and the diaphragmatic pleura, covering the anterior surface 

 of the diaphragm. The latter is broadly connected with the pulmonary 

 pleura through. the pulmonary ligament. 



The peritoneal cavity, the largest of the serous spaces, comprises in a 

 mammal a general portion, the abdominal cavity, and its posterior ex- 

 tension into the pelvis — in the male also into the sac of the testis. The 

 general relations of the cavity to the abdominal organs is indicated dia- 

 grammatically in Fig. 21. Its lining membrane, the peritoneum, is 

 divisible into two portions, the parietal peritoneum, lining the, abdominal 

 wall, and the visceral peritoneum, investing the visceral organs. Of 



the latter the kidneys encroach only 

 to a minor extent on the serous 

 lining, so that they are covered by 

 peritoneum only on their ventral sur- 

 faces. The digestive tube, on the 

 other hand, is removed to such an 

 extent from the abdominal wall that 

 the peritoneum forms a complete 

 serous coat, and is connected with 

 the parietal peritoneum of the wall 

 through a thin transparent mem- 

 brane, the mesentery. The latter 

 consists of two plates of peritoneum, 

 enclosing between them a thin layer 

 of connective tissue, the lamina 

 mesenterii propria, for the trans- 

 mission of nerves, bloodvessels and 

 lymph canals. 



As indicated above, the relations 

 of the abdominal portion of the diges- 

 tive tube are greatly modified by its 

 elongation and displacement from a 

 median position. Thus, while in the 

 embryo the common mesentery is 

 recognizable as a continuous median 

 vertical fold, in the adult it follows 

 the convolutions of the digestive tube, 

 and is therefore considered as divided 

 into corresponding parts. In many 

 cases the relations of these are greatly 

 complicated by secondary adhesions. 

 , mesentery, and descending mesocolon 

 will be recognized as parts in which a more typical arrangement is 

 retained. Moreover, in the anterior portion of the abdominal cavity the 

 peritoneum is concerned not only with the investment of two large visceral 

 structures, the stomach and the liver, but also with the formation of a lining 

 for the posterior surface of the diaphragm. Thus the general condition 

 is less simple than in the small and large intestines. The peritoneum, 



v.ty. 



Fig. 26. Diagram showing (the relation of 

 the testis to its investments: a.i., inguinal 

 ring; c.e., caput epididymidis; cr., cremaster 

 muscle; d.d., ductus deferens; g., guber- 

 naculum; mes., mesorchium; p.t.v. and 

 v.t.v., parietal and visceral layers of the tunica 

 vaginalis propria; p. v., cavity of the vaginal 

 process; s., integument of the scrotum; 

 s.v., spermatic vessels; t., testis. 



In the rabbit the mesoduodenum, 



