RAT, A REPRESENTATIVE MAMMAL 143 



is homologous to the penis of the male and is similarly erectile 

 tissue which becomes engorged with blood during sexual excitement. 

 The vaginal orifice is immediately ventral to the anus and the urinary 

 aper^ture just ventral to this, being at the base of the clitoris. 



Internally, the ovaries are located in the pelvic portion of the ab- 

 domen. They are small and flattened. The mesentery which sup- 

 ports each ovary is the mesovarium. The oviducts are rather slender 

 and less than an inch in length. The mouth of each oviduct is near 

 the ovary of that side and is called the ostium. It is funnel-shaped 

 and has a row of fingerlike fimbria around its margin. From this, 

 the tube extends to the horn of the uterus. There is no direct con- 

 nection between the ovary and oviduct, but the ostium usually 

 covers the side of the ovary through which a mature ovum is to 

 rupture in order that the germ cell will be received by the oviduct. 

 In this animal there are two horns to the uterus^ each receiving an 

 oviduct. These horns converge and almost immediately join the 

 vagina which leads to the exterior. Embryos develop in the horns 

 of the uterus. 



In summary, the germ cells are produced in the ovary, are freed 

 by rupture through its wall, are received by the ostium of the 

 oviduct, are moved through the oviduct (fertilized here, if fertilized) 

 to the horn of the uterus where the fertilized ovum (zygote) becomes 

 implanted and a placenta is formed. If not fertilized, the ovum 

 passes from the uterus to the vagina and out by way of vaginal 

 orifice. The vagina receives the penis during copulation (sexual 

 act), and the spermatozoa are discharged from the penis here. 



Male Reproductive Organs. — Included here are the penis, scrotum, 

 testes, epididymis, vasa deferentia, seminal vesicle, urethra, prostate 

 glands, and Cowper's glands. The penis is composed of erectile 

 tissue and covered by the integument. The erectile tissue is en- 

 gorged with blood during sexual excitement and causes the organ 

 to become enlarged and rigid. The parts of the penis are the hase 

 or bulb at the proximal end, the body, and the glans or head at the 

 distal end. The prepuce is the loose skin which covers the glans. 



The scrotum is a prominent sac in the perineal region of the male. 

 Internally it is divided into two pouches which are strictly out- 

 pushings of the coelomic cavity in that the peritoneum continues 

 through each inguinal canal to line each of these pouches. The 

 testes descend from the abdomen to the scrotum during breeding 



