The Serous Cavities. 51 



passing from the dorsal wall, successively invests the spleen, the 

 stomach, and the liver, and is reflected from the last-named structure 

 to the diaphragm and the ventral body-wall through the coronary, 

 triangular, and falciform ligaments. Its gastric portion is differentiated 

 into the mesogastrium (phrenicosplenic and gastrolienal ligaments), the 

 greater omentum, and the lesser omentum. Similarly, in the posterior 

 part of the body the peritoneum passes from the rectum to the urinary 

 bladder, enclosing also in the female the vagina. It is then reflected to 

 the ventral body-wall as the middle umbilical fold. 



In the male, as indicated in the accompanying diagram (Fig. 26), the 

 peritoneal relations of the testis are greatly modified by the migration 

 of the organ from an abdominal to a scrotal position. The entire sac 

 lodging the testis is an evaginated portion of the abdominal wall, and 

 since in the rabbit the cavity is widely open throughout life to the 

 abdominal cavity, the lining membrane — that designated as the parietal 

 layer of the tunica vaginalis propria— is continuous with the parietal 

 peritoneum of the abdomen, and thus represents a permanent vaginal 

 process. Like other structures of the abdominal cavity, the testis itself 

 is covered by peritoneum, the latter being designated as the visceral 

 layer of the tunica vaginalis propria. This investment is connected with 

 the parietal layer by the mesorchium, and in the rabbit it will be 

 observed that the latter is chiefly attached forwards on the dorsal wall 

 of the abdomen, i.e., in a position indicating the original situation of 

 the testis itself. 



In the female the ovary is closely associated with the -dorsal wall 

 of the abdomen, and its supporting peritoneum, the mesovarium, is in- 

 significant. Its duct in passing backward, however, becomes greatly 

 displaced from a dorsal position, and thus comes to be supported by a 

 broad fold of peritoneum. The latter is considered to consist of two 

 portions, one, the mesosalpinx, being the support of the uterine tube, 

 the other, the mesometrium, that of the uterus. The entire fold, how- 

 ever, forms a continuous structure, and is known in this relation as the 

 broad ligament. 



REGIONAL SECTIONS. 



The following plate-figures (I-VIII) are from characteristic sections 

 of a rabbit-foetus of 56mm., and may be used either in connection with 

 the general features of topography as outlined above, or for the identi- 

 fication of various minor structures appearing in the dissection. 



Certain points regarding the sections are perhaps worthy of notice. 

 First, in the longitudinal section illustrated in Plates I and II it will be 

 noticed that paired structures frequently appear; this being because of 

 the fact that the section is not exactly median, at least in certain places. 

 Secondly, in using sections of the foetus for gross anatomical features 

 it is necessary to make allowance in some cases for the different propor- 

 tions of organs, and consequent slight differences in position, in the 

 foetal as compared with the adult condition. .Finally, many of the 

 features appearing in the original sections are such as could not be repro- 

 duced in the plates, although they are indicated in the accompanying 

 skeleton figures, and may be referred to in this way. 



