THE PENIS. 



1969 



Fig. 1677. 



Deep dorsal vein 



Subcutaneous 

 tissue 



Skin 



Tunica albuginea 



Septum 



miiscle, circularly, longitudinally, and obliquely disposed, occupy the connective-tissue 

 trabecule and plates separating the venous lacunae, around which they form imperfect 

 layers of contractile tissue. The trabecular muscle is most developed within the cav- 

 ernous and spongy bodies and least so within the glans. 



The arteries conveying blood to the cylinders of erectile tissue are of two kinds, 

 — those nourishing the tissues themselves {vasa nutritia) and those carrying blood to 

 the venous lacunse. The latter are connected with the arteries either direcdy by 

 minute channels or through intervening capillaries. Within the trabeculae of the 

 deeper parts of the erectile masses the deep arteries of the penis give off short, tortuous 

 branches {^arterice helicince), about 2 mm. in length, that project into the blood-spaces 

 with which they direcdy communicate by minute openings at their ends. Notwith- 

 standing their exceptional development in man, the fact that the helicine arteries are 

 wanting in many mammals shows that they are not essential, although advantageous, 

 for erection. The arteries of the erectile tissue are distinguished by the unusual thick- 

 ness of the circular muscle within their walls. In places the indma likewise exhibits 

 excessive thickness. Since the increase is not uniform but local, it leads to the pro- 

 duction of cushion- 

 like elevations that 

 encroach upon and 

 even temporarily oc- 

 clude the lumen of the 

 arteries. 



The blood-spaces 

 or lacunce that occupy 

 the interstices between 

 the trabeculae are to 

 be regarded as venous 

 net-works which com- 

 municate with the ar- 

 teries, on the one 

 hand, and with the 

 radicles forming the 

 veins, on the other. 

 Their form and size 

 evidently depend 

 upon the degree of 

 distention, when con- 

 taining little blood the 

 spaces being often 

 mere slits or irregu- 

 larly stellate clefts, 

 while when filled they 

 become more cylin- 

 drical in form. In a general way three districts may be distinguished : {a') a narrow 

 outer periphe7'al zone of almost capillary spaces, for the most part narrow and trian- 

 gular in outline ; {b~) an inyier peripheral zone of larger spaces of uncertain form and 

 from .15-20 mm. in diameter ; and (r) a central zone oi still more extensive spaces, 

 which in places attain a diameter of one or more millimetres and are enclosed by rela- 

 tively thin intervening lamellae and trabeculae. Since their expansion is usually 

 greater in one direction, the general form of the larger and deeper lacunae is often ap- 

 proximately cylindrical. Within the corpus spongiosum in the immediate vicinity of 

 the urethra the blood-spaces are somewhat concentrically disposed owing to the feeble 

 development of the radial lamellae (Eberth). The spongy body is further distin- 

 guished by the robustness of its trabeculae and the consequent reduction in the size of 

 the blood-spaces. Beyond the single layer of endothelial plates, the lacunae do not 

 possess a distinct wall other than the fibro-muscular tissue of the surrounding trabeculae. 



The deep veins draining the cylinders of erectile tissue do not directly open into 

 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 in fact extensions. The tributaries of the 



124 



Superficial 



fascia 



Corpus 

 cavernosutn 



Urethra 



corpus 

 spongiosum 



Transverse section of penis of child. X lo. 



