MALE ORGANS OF REPRODUCTION 



505 



where they are most abundant near the root of the organ. The ar- 

 terioles from which they are derived end by arborization in the con- 

 nective tissue framework, their terminal twigs entering fibrous processes 

 which project into the venous sinuses and are frequently bound down 

 by delicate fibrous bands which unite their extremity to the wall of the 

 sinus and produce the characteristic looped condition when the villus- 

 like projection is distended by the injection of its arteriole. When 

 partially injected the helicine arteries appear to end blindly, but when 



f.a. 



FIG. 448. THE ERECTILE TISSUE OF THE PENIS. 



c r, peripheral capillary plexus; t o, tunica albuginea; v s, venous spaces; z, bands 

 of smooth muscle and vascular connective tissue. X 30. (After Kolliker.) 



completely distended they pour their contents -into the venous sinuses. 

 The venous spaces at the periphery of the erectile body are relatively 

 narrow and the intervening trabeculae are thick; toward the axis of the 

 body the sinuses become broader and occupy a relatively greater portion 

 of the tissue. Here, also, their long axis, except in the corpus spongi- 

 osum, frequently lies in the transverse axis of the penis. Both the 

 arteries and the veins of the erectile tissue possess very thick muscular 

 walls, and in both, the intima becomes locally thickened by accumula- 

 tions of longitudinal muscles and elastic tissue bulging into the lumen ; 

 these modifications are less pronounced in the veins than in the arteries, 



