290 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



Now cut through the pubic and ischial symphyses and spread the legs well 

 apart. Trace the urethra, the vagina, and the rectum posteriorly. The urethra 

 lies at first on the ventral face of the vagina to which it is bound by tissue; it 

 then unites with the vagina to form a common tube, the urogenital canal or sinus.. 

 Dissect this free and lift it out and follow it to the urogenital aperture. Cut 

 open the urogenital aperture and note the free posterior end, or glans, of the 

 clitoris, projecting into the cavity in the rabbit. Free the rectum from the uro- 

 genital canal and follow it to the anus. Along its sides in the rabbit are a pair of 

 elongated glands, the anal glands. In the cat the rounded anal glands or sacs 

 are situated one at each side of the rectum, just internal to the anus. 



Draw the female urogenital system. 



Cut open the vagina. In the rabbit note the external uterine orifice 

 with raised fringed lips by means of which each uterus opens into the vagina. 

 The rabbit uterus is of the duplex type (Fig. 63 B, p. 278). In the cat the body 

 is divided into lateral halves by a median partition, a horn opening to each side 

 of the partition. The cat uterus is of the bipartite type (Fig. 63C). The lower 

 end of the uterus, called the cervix, projects into the vagina by a fold. The 

 opening of the body of the uterus into the vagina is the external uterine orifice. 



3. The male reproductive system. — The external parts or external genitalia 

 were described with the external anatomy. Review this (p. 29) . The two testes 

 are lodged in the scrotal sac which is divided into two compartments by an 

 internal partition. Cut through the skin over and in front of one testis, exposing 

 the testis as an oval white body. Clear away the connective tissue anterior 

 to the testis and find a white cord, the spermatic cord, passing forward and entering 

 the peritoneal cavity through a canal called the inguinal canal. The external 

 end of this canal is the external inguinal ring; the internal end, the internal 

 inguinal ring. Trace the spermatic cord by cutting open the canal. 



The spermatic cord contains a white duct, the male duct or vas deferens, 

 and the blood vessels and nerves of the testis. The two vasa deferentia turn 

 toward the median line, loop over the ventral surfaces of the ureters, and dis- 

 appear on the dorsal surface of the urethra. 



It is now necessary to explain these relations of the testes and their ducts. In the verte- 

 brates previously studied the testes lie within the peritoneal cavity, but in most adult mammals 

 they are situated posterior to this cavity. In the embryos of male mammals, however, the 

 testes lie within the peritoneal cavity; subsequently they descend caudad. There is first 

 formed a sac of the body wall, the scrotal sac, which contains all of the layers of the body wall- 

 skin, muscles, and peritoneum — and incloses a portion of the coelom, the vaginal sac. The 

 testes then descend into the scrotal sac, as shown in Figure 65, carrying with them their ducts, 

 the nerves, blood vessels, etc. The canal along which the descent occurs later narrows and 

 eventually is completely obliterated in the higher mammals but in some remains open. (See 

 K> P- 373-) A new canal, the inguinal canal, is later secondarily formed around the spermatic 

 cord. The descent of the testes explains the peculiar looping of the vasa deferentia over the 

 ureters and the course of the internal spermatic vein. Neither the cause of the descent of the 

 testes nor its purpose are known. 



