1116 UROGENITAL SYSTEM. 
whose interspaces communicate freely with one another, and are filled with blood. 
These blood-containing spaces lead directly into the veins of the penis, and like the veins 
have a lining of flat endothelial cells. The size of the penis varies with the amount of 
blood in this cavernous tissue. The structure of the corpus spongiosum resembles that 
of the corpora cavernosa, but the fibrous coat is much thinner, and the trabeculie are 
finer. Smooth muscle fibres surround the urethra as it traverses the corpus spongiosum 
(Fig. 762). 
In some mammals, such as the walrus, dog, bear, baboon, etc., a bone called the os penis is 
developed in the septum which intervenes between the corpora cavernosa. 
Vessels and Nerves of the Penis.—The penis receives its arterial supply from branches of 
the internal pudic artery. The erectile tissue of the corpora cavernosa is supplied chiefly by the 
deep arteries of the penis, while that of the corpus spongiosum receives its arterial supply from 
the artery to the bulb. Branches of the dorsal artery of the penis piercing the fibrous coat of 
the corpora cavernosa furnish additional twigs to the erectile tissue of these structures. The 
glans receives its chief blood supply from branches of the dorsal artery. The small branches of 
these arteries run in the trabeculz of the erectile tissue, and the capillaries, into which they 
lead, open directly into the cavernous venous spaces. As they lie in the finer trabecule, the 
smaller branches often present a peculiar twisted appearance, and hence the name helicine 
arteries (arteriz helicinse) is sometimes applied to them. 
The veins with which the cavernous spaces communicate carry the blood, for the most part, 
either directly into the prostatic plexus, or into the dorsal vein, and so to the prostatic plexus. 
The dorsal vein of the penis begins in tributaries from the glans and prepuce, and hes in the 
groove between the corpora cavernosa as it ascends to pass beneath the sub-pubic ligament and 
join the prostatic plexus. On each side of it lies the dorsal artery, and still further from the 
middle line the dorsal nerve (Fig. 762). 
The nerve-supply of the penis is derived from the internal pudic nerve and from the hypo- 
gastric plexus The branches of the internal pudic are the dorsal nerve of the penis, and 
branches from the superficial perineal nerves. These supply the cutaneous structures of the 
penis, while the sympathetic filaments from the hypogastric plexus, which reach the penis 
through the prostatic plexus, end in the erectile tissue. 
THE PROSTATE. 
The prostate (prostata) is a partly glandular, partly muscular organ of a dark 
brown-red colour which surrounds the beginning of the urethra in the male. It 
lies within the pelvis, and is enclosed by a dense capsule derived from the pelvic 
fascia. The common ejaculatory ducts traverse the prostate in their course down- 
wards and forwards to join the urethra as it descends through the gland (Fig. 
755). The size of the prostate varies considerably in different individuals, but 
its transverse or longest diameter is usually from one and a quarter to one and a 
half inches, its antero-posterior diameter about three quarters of an inch, and its 
vertical diameter about one and a quarter inches. Superficially the prostate is 
/> Ureter 
Vas deferens.<] 
Upper surface 
Ureter of bladder 
Vas ( 
deferens 
«Seminal _ ' 
vesicle Urachus Seminal < 
vesicle Z 
Y Urachus 
Infero-lateral 
area of bladder 
Lateral aspect 
of prostate Lateral 
; aspect of 
@— Urethra prostate 
Infero-lateral 
area of bladder 
Urethra 
A B 
Fic. 763.—BLADDER, PROSTATE, AND SEMINAL VESICLES VIEWED FROM THE OUTER SIDE, 
Drawn from specimens hardened im situ. 
separated from the bladder by deep wide lateral grooves directed downwards and 
forwards, and by a narrow posterior groove which is horizontal. 
In connexion with the prostate we describe an apex which is directed down- 
wards, a base looking upwards, a posterior, and two lateral surfaces. The general 
outline of the organ has been often compared with that of a Spanish chestnut. 
il 
