MALE REPRODUCTIVE ORGANS. 7 



The male urethra leads from the bladder to the end of 

 the penis, where it terminates in an opening, the meatus 

 urinarius. It is described by anatomists as made up of three 

 portions, the prostatic, the membranous, and the spongy. 

 The first is surrounded by the prostate gland and receives 

 the ejaculatory ducts. On its posterior wall, close to the 

 bladder, is an elevation containing erectile tissue (see below) 

 and supposed to be dilated during sexual congress, so as to 

 cut off the passage to the urinary receptacle. On this crest 

 is an opening leading into a small recess, the utricle, which 

 is of interest, since the study of Embryology shows it to be 

 an undeveloped male uterus. The succeeding membranous 

 portion of the urethra is about 1.8 cm. (f inch) long; the 

 spongy portion lies in the penis. 



The penis is composed mainly of erectile tissue, i.e. 

 tissues so arranged as to inclose cavities which can be dis- 

 tended by blood. Covered outside by the skin, internally 

 it is made up of three elongated cylindrical masses, two of 

 which, the corpora cavernosa, lie on its anterior side; the 

 third, the corpus spongiosum, surrounds the urethra and 

 lies on the posterior side of the organ for most of its length; 

 it, however, alone forms the terminal dilatation, OY glans, of 

 the penis. Each corpus cavernosum is closely united to its 

 fellow in the middle line and extends from the pubic bones, 

 to which it is attached behind, to the glans penis in front. 

 It is enveloped in a dense connective-tissue capsule from 

 which numerous bars, containing white fibrous, elastic, and 

 unstriped muscular tissues, radiate and intersect in all 

 directions, dividing its interior into many irregular cham- 

 bers called venous sinuses. Into these arteries convey blood, 

 which is carried off by veins springing from them. 



The arteries of the penis are supplied with vaso-dilator 

 nerves (p. 257), the nervi engentes, from the sacral plexus 

 (p. 162). Under certain conditions these are stimulated 

 and, the arteries expanding, blood is poured into the 

 venous sinuses faster than the veins drain it off ; the latter 

 are probably also at the same time compressed where they 

 leave the penis by the contraction of certain muscles passing 

 over them; the organ then becomes distended, rigid, and 



