THE PENIS. 1013 



elastic fibres, and plain muscular fibres. In them are contained numerous 

 arteries and nerves. 



The component fibres of which the trabeculge are composed are larger and 

 stronger round the circumference than at the centre of the corpora cavernosa ; 

 they are also thicker behind than in front. The interspaces, on the contrary, are 

 larger at the centre than at the circumference, their long diameter being directed 

 transversely ; they are largest anteriorly. They are occupied by venous blood, 

 and are lined by a layer of flattened cells similar to the endothelial lining of veins. 



The whole of the structure of the corpora cavernosa contained within the 

 fibrous sheath consists, therefore, of a sponge-like tissue of areolar spaces freely 

 communicating with each other and filled with venous blood. The spaces may 

 therefore be regarded as large cavernous veins. 



The arteries bringing the blood to these spaces are the arteries of the corpora 

 cavernosa and branches from the dorsal artery of the penis, which perforate the 

 fibrous capsule, along the upper surface, especially near the fore part of the 

 organ. 



These arteries on entering the cavernous structure divide into branches which 

 are supported and enclosed by the trabeculge. Some of these terminate in a 

 capillary network, the branches of which open directly into the cavernous spaces ; 

 others assume a tendril-like appearance, and form convoluted and somewhat 

 dilated vessels, which were named by Muller helicine arteries. They project 

 into the spaces, and from them are given off small capillary branches to supply 

 the trabectilar structure. They are bound down in the spaces by fine fibrous 

 processes, and are more abundant in the back part of the corpora cavernosa 

 (Fig. 564). 



The blood from the cavernous spaces is returned by a series of vessels, some 

 of which emerge in considerable numbers from the base of the glans penis and 



FIG. 564. From the peripheral portion of the corpus cavernosum. penis under a low magnifying power. 

 (Copied from Langer.) 1. a. Capillary network, b. Cavernous spaces. 2. Connection of the arterial twigs (a) 

 with the cavernous spaces. 



converge on the dorsum of the organ to form the dorsal vein ; others pass out on 

 the upper surface of the corpora cavernosa and join the dorsal vein ; some emerge 

 from the under surface of the corpora cavernosa, and, receiving branches from the 

 corpus spongiosum, wind round the sides of the penis to terminate in the dorsal 

 vein; but the greater number pass out at the root of the penis and join the 

 prostatic plexus. 



The Corpus Spongiosum encloses the urethra, and is situated in the groove on 

 the under surface of the corpora cavernosa. It commences posteriorly below the 

 superficial layer of the triangular ligament of the urethra, between the diverging 

 crura of the corpora cavernosa, where it forms a rounded enlargement, the bulb, 

 and terminates anteriorly in another expansion, the glans penis, which overlaps 

 the anterior rounded extremity of the corpora cavernosa. The central portion, 

 or body of the corpus spongiosum, is cylindrical, and tapers slightly from behind 

 forward. 



The bulb varies in size in different subjects; it receives a fibrous investment 



