13 g8 THE URINOGENITAL ORGANS 



lobes of that gland, and along the side of the sinus pocularis, to terminate by a 

 separate slit-like orifice close to the margins of the sinus. The ducts diminish 

 in size and also converge toward their terminations. 



Structure. The coats of the ejaculatory ducts are extremely thin. They are an outer 

 fibrous layer, which is almost entirely lost after the entrance of the duct into the prostate; 

 a layer of muscle fibres, consisting of an outer thin circular and an inner longitudinal layer; and 

 the mucous membrane, lined by simple columnar epithelial cells. 



THE PENIS (Figs. 1138, 1139). 



The penis is a pendulous organ suspended from the front and sides of the pubic 

 arch and containing the greater part of the urethra. In the flaccid condition 

 it is cylindrical in shape, but when erect assumes the form of a triangular prism 

 with rounded sides, one side of the prism forming the dorsum. It is composed of 

 three cylindrical masses of erectile tissue bound together by fibrous tissue and 

 covered with skin. Two of the masses are lateral, and are known as the corpora 

 cavernosa; the third is median, and is termed the corpus spongiosum (Figs. 1138 and 

 1146). 



The two corpora cavernosa (corpora cavernosa penis} (Figs. 1138 and 1139) 

 form the greater part of the body of the penis. They consist of two fibrous 

 cylindrical tubes, placed side by side, and intimately connected along the median 

 line for their anterior three-fourths, while at their back part they separate from 

 each other to form the crura penis, which are two strong tapering fibrous processes 

 or roots firmly connected to the rami of the os pubis and ischium (Figs. 1138 and 

 1 139). Each crus commences by a blunt-pointed process in front of the tuberosity 

 of the ischium, and before its junction with its fellow to form the body of the penis 

 it presents a slight enlargement, named by Kobelt the bulb of the corpus cavernosum. 

 Just beyond this point they become constricted, and retain an equal diameter 

 to their anterior extremity, where they form a single rounded end (digital pro- 

 cess} which is received into a fossa in the base of the glans penis (Fig. 1138). 

 A median groove on the upper surface lodges the dorsal arteries, nerves, and veins 

 of the penis (Figs. 1144 and 1146), and the groove on the under surface receives 

 the corpus spongiosum (Fig. 1138). 



The corpora cavernosa are surrounded by a strong fibrous envelope (tunica 

 albugined} consisting of superficial and deep fibres. The superficial fibres are 

 longitudinal in direction, being common to the two corpora cavernosa, and in- 

 vesting them in a common covering; the other, deep, circular in direction, and 

 being proper to each corpus cavernosum. The internal circular fibres of the two 

 corpora cavernosa form, by their junction in the mesal plane, an incomplete 

 partition or septum (septum penis) between the two bodies. This is thick and 

 complete behind, but in front it is incomplete, and consists of a number of vertical 

 bands, which are arranged like the teeth of a comb. It is therefore named the 

 septum pectiniforme. These bands extend between the dorsal and the urethral 

 surface of the corpora cavernosa. The fibrous investment of the corpora cavernosa 

 is extremely dense, of considerable thickness, and consists of bundles of shining 

 white fibres, with an admixture of well-developed elastic fibres, so that it is 

 possessed of great elasticity. 



The corpus spongiosum (corpus cavernosum urethrae) (Figs. 1138 and 1139) 

 contains the urethra, and is situated in the groove on the under surface of the 

 corpora cavernosa penis. Behind, it is expanded to form the urethral bulb (bulbus 

 urethrae} and lies in apposition with the superficial layer of the triangular ligament, 

 from which it receives a fibrous investment. The urethra enters the bulb nearer 

 to the upper than to the lower surface. On the latter there is a depressed 



