MALE GENITAL ORGANS OF THE DOG 595 
The cavernous spaces of the g!ans penis are venous in character. Von Frey has shown that 
the spaces of the pars longa are continuous with veins which come from the penile layer of the pre- 
nice, and have no arterial blood supply. The erectile tissue of the bulbus glandis receives its 
lood by veins which come from the pars longa. This arrangement is considered to account for 
the erection of the bulbus during copulation, and the slowness with which erection subsides. 
The prepuce forms a complete sheath around the anterior part of the penis. 
The outer layer is ordinary integument. The inner layers are thin, reddish in 
color, and glandless. The penile layer is closely attached to the pars longa glandis, 
more loosely to the bulbus glandis. There are many lymph nodules in these layers, 
which are specially large and often prominent in the fundus of the preputial cavity. 
The protractor muscles arise in the xiphoid region and decussate posteriorly around 
the extremity of the prepuce. 
The pelvic part of the urethra is relatively long. Its first part is enclosed in 
the prostate.t At the ischial arch the urethra has a well-developed bulb, formed 
by an enlargement here of the corpus cavernosum urethre. It is divided by a 
median furrow and septum (Septum bulbi urethr) into two lateral lobes or hemis- 
pheres (Hemispheria bulbi urethrz), and is covered by the strong but short bulbo- 
cavernosus muscle. The other erectile bodies have been described. The urethral 
muscle is very strong; it encircles the urethra from the prostate backward and has 
a median raphé dorsally. The ischio-urethral muscle arises from the tuber ischii 
and ends on a fibrous ring at the symphysis ischii which encircles the dorsal veins 
of the penis. 
1This is clinically important, since enlargement of the prostate may interfere with mic- 
turition. 
