242 



THE CONTINUITY OF THE RACE 



and the base of the urethra and opens into the latter, as do the ducts of 

 the small Cowper's glands. The functions of the prostate gland and 

 Cowper's glands are not entirely understood, though they probably 

 contribute fluid to the semen; they are not, however, essential for 

 reproduction. 



The distal portion of the urethra traverses the erectile copulatory 

 organ, the penis. This organ is composed chiefly of three corpora cavernosa, 

 two dorsal and one ventral, the latter enclosing the urethra and expanding 



ureter 



body cavity 



vas deferens 



symphysis 

 pubis 



urethra 



corpora 

 cavernosa 



testis 



scrotum 



arge 

 intestine 



seminal 

 vesicle 



prostate 

 gland 



anus 



Fig. 16.1. The male reproductive system. 



at its distal end into the glans penis. The two dorsal corpora cavernosa 

 diverge within the body and are attached to the pubic bones. The corpora 

 cavernosa contain large blood spaces; under the influence of sexual 

 excitement, the arteries carrying blood to the organ are dilated and the 

 veins are constricted at its base, causing the spaces to fill with blood under 

 pressure and the penis to become erect. Ejection of the semen is brought 

 about chiefly by rhythmic contractions of the vasa deferentia and the 

 bulbocavernosus muscle; the latter encloses the intrapelvic basal portion 

 of the ventral corpus cavernosum. 



The reproductive system of the female. The paired ovaries are the 

 parts of the female reproductive system in which the germ cells are housed 

 and in which the mature germ cells, or eggs, are produced. The ovaries 



