24 o NORMAL HISTOLOGY. 



connected with the arteries either directly, by minute channels, or by inter- 

 vening capillaries. Within the trabeculae of the deeper parts of the erectile 

 masses, short tortuous branches, arteria helicince, are given off; in the 

 relaxed condition these are twisted and project into the blood-spaces. Both 

 the arteriae nutritiae and helicinae finally directly communicate by minute 

 canals with the deeper lacunae of the cavernous tissue. The arteries of the 

 erectile tissue are remarkable for the unusual thickness of their circular 



Central blood-spaces Inner peripheral spaces Outer peripheral spaces 



Trabeculae Bundles of muscle Dense fibrous tissue of 



tunica albuginea 



FIG. 291. Transverse section through periphery of corpus cavernosum, showing erectile tissue. X 50 



muscle. In places the intima likewise exhibits excessive thickness due to 

 accumulation of longitudinal muscle, such local augmentations producing 

 cushion-like bulgings that encroach upon the lumina of the arteries. 



The lacunae, the blood-spaces that occupy the interstices between the 

 trabeculae, are regarded as venous networks which communicate with the 

 arteries, on the one hand, and with the radicles forming the veins on the 

 other. Beyond the single layer of lining endothelial plates they possess no 

 special wall. Their form and size depend upon the degree of distention, 

 when containing little blood being often mere slits or irregular stellate clefts, 

 while when filled they become more cylindrical. Three tracts may be dis- 

 tinguished: (a) a narrow outer peripheral zone of almost capillary spaces, 

 for the most part narrow and triangular in outline; (3) an inner peripheral 

 zone of larger spaces of uncertain form and from .15-. 20 mm. in diameter; 

 and (f) a central zone of still more extensive spaces (1-3 mm.) enclosed by 

 relatively thin lamellae and trabeculae. The deep veins draining the erectile 

 cylinders do not directly open from the blood-spaces, but are formed by 

 tributaries of various size that begin as apertures in the walls of the lacunae 

 of which they are extensions. The tributaries of the superficial venous 

 trunks, as the dorsal veins, arise chiefly from the venous networks of the 

 peripheral zone. The veins possess unusually strong muscular coats and 



