THE MALE GENITAL ORGANS. 371 



and lying side by side, and the corpus spongiosum, surrounding 

 the urethra and lying below and between the corpora cavernosa. 

 The two latter are surrounded by a dense connective-tissue sheath, 

 the tunica albuginea. These erectile bodies are surrounded by a 

 thin layer of skin, containing no adipose tissue and no hair-follicles. 

 The corpus spongiosum is enlarged anteriorly to form the glans 

 penis. 



The principal substance of the erectile bodies is the so-called 

 erectile tissue : septa and trabeculae, consisting of connective 

 tissue, elastic fibers, and smooth muscle-cells inclosing a sys- 

 tem of communicating spaces. These latter may be regarded as 

 venous sinuses, the walls of which, lined by endothelial cells, are 

 in apposition to the erectile tissue. Under certain conditions the 

 venous sinuses are distended with blood, but normally they are in 

 a collapsed state and form fissures which simulate the clefts found 

 in ordinary connective tissue. In other words, there is here such 

 an arrangement of the blood-vessels within the erectile tissue that 

 the circulation may be carried on with or without the aid of the 

 cavernous spaces. The arteries of the corpora cavernosa possess 

 an especially well-developed musculature. They ramify through- 

 out the trabeculae and septa of the erectile tissue and break up 

 within the septa into a coarsely meshed plexus of capillaries. A few 

 of these arteries empty directly into the cavernous spaces. On the 

 other hand, the arteries give off a rich and narrow-meshed capillary 

 network immediately beneath the tunica albuginea. This is in com- 

 munication with a deeper and denser venous network, which, in turn, 

 gradually empties into the venous sinuses. Aside from these there 

 are anastomoses between the arterial and venous capillaries, which 

 later communicate with the venous network just mentioned. The 

 biood current, regulated as it thus is, may pass either through 

 the capillaries alone, or may divide and flow through both these 

 and the venous sinuses. These conditions explain both the erec- 

 tile and quiescent state of the penis. The relations are somewhat 

 different in the corpus spongiosum urethrae and in the glans penis. 

 In the corpus spongiosum the arteries do not open directly into 

 the venous spaces, but break up first into capillaries. In the sub- 

 mucosa of the urethra there is found a rich venous plexus. In the 

 glands the arteries end in capillaries which pass over into veins with 

 well-developed muscular walls. The blood is collected by means 

 of the venae emissariae which empty into the vena dorsalis penis and 

 into the venae profundae. 



The epithelium of the urethra varies in the several regions. The 

 prostatic portion possesses an epithelium similar to that of the 

 bladder. In the membranous portion, the epithelium may be simi- 

 lar to that found in the prostatic portion, but more often pre- 

 sents the appearance of a pseudostratifiecl epithelium with two or 

 three layers of nuclei. The cavernous region is lined by pseudo- 

 stratified epithelium, except in the fossa navicularis, where a 

 stratified squamous epithelium is found. Between the fibro-elastic 



