G18 



COMPARATIVE ANATOMY. 



The apparatus thus formed is variously modified in different 

 parts. The testes do not retain their primitive position anteriorly 

 to the kidneys in any Mammals except the Monotremata. In the 

 Cetacea, Hyrax, Elephas, and various Edentata, they are placed a 

 little to the side of, or below the kidneys. In others they are found in 



the inguinal region of the ab- 

 dominal wall, which they pass 

 through (many Rodents, the 

 Camelida3, and various Car- 

 nivora [Lutra, Viverra]). In 

 others, finally, they travel still 

 further by means of the ingui- 

 nal canal, descending through 

 the wall of the abdomen iuto 

 a diverticulum, the scrotum, 

 which is formed from the in- 

 tegument. The space which is 

 formed (canalis vaginalis) when 

 the testis passes into the scro- 

 tum, by the peritoneum which 

 grows out with the descending 

 testis, is permanently open in 

 most Mammals, so that the 

 cavity around the testis is in 

 communication with the ab- 

 dominal cavity. As the testes 

 pass down the inguinal canal 

 the abdominal wall is driven 

 in front of them. When the 

 vaginal canal remains open 

 the testes may return again 

 to the abdominal cavity; this 

 ordinarily happens in many 

 Mammals during the breeding 

 season (e.g. Marsupialia, Ro- 

 dentia, Chiroptera, Insectivora, 

 etc.). The scrotum of the 

 Marsupialia is remarkable for 

 its position in front of the 

 genital orifice. It is a special 

 structure, while in the Mono- 

 delphia the scrotum is de- 

 veloped from the boundary of 

 the primitive urogenital orifice. 

 The lower end of the vas deferens is always simple in the 

 Monotremata and Marsupialia, Carnivora and Cetacea. In the rest 

 it gives rise to glandular structures, which are known as "vesiculas 

 seminales," as the sperm may be collected in them (yl). These 

 organs are greatly develoj^ed in the Insectivora and many Rodents; 



Fig. 353. I Urinary and generative organs 

 of Cricetus vulgaris. B Kidneys. 

 u Ureter, v Urinary bladder. T Testes. 

 Sp Vasa spermatica. il Vas deferens, gl 

 Vesicular seminales. gV gl" Prostatic glands. 

 m Muscular portion of the urogenital sinus. 

 ic Corpus cavernosum penis, be Corp. cav. 

 urethras. c Cowper's glands. t Tyson's 

 glands, p Prepuce, g Glans penis. II Neck 

 of the bladder, and commencement of the 

 urogenital sinus, opened in front. * Opening 

 of the ductus ejaculatorii. Ill Glans penis 

 seen from in front. 



