PENIS. 803 



riorly, 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 forwards. 



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

 from the anterior layer of the deep perineal fascia, and is surrounded by the 

 Accelerator Urinse muscle. The urethra enters the bulb nearer its upper than 

 its lower surface, being surrounded by a layer of erectile tissue, a thin prolon- 

 gation of which is continued backwards round the membranous and prostatic 

 portions of the canal to the neck of the bladder, lying immediately beneath 

 the mucous membrane. The portion of the bulb below the urethra presents a 

 partial division into two lobes, being marked externally by a linear raphe, 

 whilst internally there projects inwards for a short distance a thin fibrous sep- 

 tum, more distinct in early life. 



Structure. The corpus spongiosum consists of a strong fibrous envelope, in- 

 closing a trabecular structure, which contains in its meshes erectile tissue. The 

 fibrous envelope is thinner, whiter in color, and more elastic than that of the 

 corpus cavernosum. The trabeculee are delicate, uniform in size, and the meshes 

 between them small ; their long diameter, for the most part, corresponding with 

 that of the penis. A thin layer of muscular fibres, continuous behind with those 

 of the bladder, forms part of the outer coat of the corpus spongiosum. 



Erectile tissue consists essentially of an intricate venous plexus, lodged in the 

 interspaces between the trabecula3. The veins forming this plexus are so 

 numerous, and communicate so freely with one another, as to present a cellular 

 appearance when examined by means of a section ; their walls are extremely 

 thin, and lined by squamous epithelium. The veins are smaller in the glans 

 penis, corpus spongiosum, and circumference of the corpora cavernosa, than in 

 the central part of the latter, where they are of large size, and much dilated. 

 They return the blood by a series of vessels, some of which emerge in con- 

 siderable numbers from the base of the glans penis, and 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, arid, receiving branches from the corpus spon- 

 giosum, 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 and pudendal veins. 



The arteries of the penis are derived from the internal pudic. Those supplying 

 the corpora cavernosa are the arteries of the corpora cavernosa, and branches 

 from the dorsal artery of the penis, which perforate the fibrous capsule near the 

 fore part of the organ. Those to the corpus spongiosum are the arteries of the 

 bulb. Additional branches are described, by Kobelt, as arising from the trunk 

 of the internal pudic ; they enter the bulbous enlargements on the corpora ca- 

 vernosa and corpus spongiosum. The arteries, on entering the cavernous struc- 

 ture, divide into branches, which are supported and inclosed by the trabeculse; 

 according to Miiller, some of these branches terminate in a capillary network, 

 which communicates with the veins as in other parts; whilst others are more 

 convoluted, and assume a tendril-like appearance ; hence the name, helicine 

 arteries, which is given to these vessels. The helicine arteries are more abund- 

 ant in the back part of the corpora cavernosa and corpus spongiosum ; they 

 have not been seen in the glans penis. They are small twigs, given off in 

 bunches from the sides of the arteries as they lie on the trabecula3, and they 

 terminate in dilated extremities hanging down into the cavity of a vein. 

 Whether the extremities of the twigs are open or closed, appears uncertain. 

 The existence of these vessels is denied by Yalentin, who describes the smallest 

 branches of the arteries as terminating by wide, funnel-shaped orifices, which 

 open directly into the venous cavities. 



The lymphatics of the penis consist of a superficial and deep set; the former 

 terminate in the inguinal glands ; the latter emerge from the corpora cavernosa 



