Page 541 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

516 CHAPTER 2

VetBooks.ir PENIS AND PREPUCE (FIG. 2.125) the glans penis and is surrounded by an invagina-
tion known as the fossa glandis.
The penis of the stallion is musculocavernous in
Ventral to the urethra and along the entire length
type and can be divided anatomically into a root, of the penis is the bulbospongiosus muscle. Arising
a body and a glans penis. The penis is supported from the urethralis muscle, its smooth rhythmic
at its root by the paired suspensory ligaments of contractions assist in moving the penile urethral
the penis and the ischiocavernosus muscles. The contents (semen and urine) distally. Rhythmic
penile root arises at the ischial arch in the form of pulsations of the bulbospongiosus muscle are dis-
two crura, which fuse distally to form the single tinctly felt during ejaculation if a hand is placed on
and dorsal corpus cavernosum penis (CCP), and it the ventral aspect of the penis during collection/
is enclosed by a thick tunica albuginea. The cavern- natural service. The paired retractor penis muscles
ous spaces making up the erectile tissue of the penis also run ventrally along the length of the penis and
are the corpus cavernosum, corpus spongiosum and attach at the glans penis. These smooth muscles
corpus spongiosum glandis. Engorgement of these function to return the penis to the sheath following
spaces with blood from branches of the internal detumescence.
and external pudendal arteries and the obturator The prepuce is formed by a double fold of skin
arteries is responsible for erection. The cavernous and resembles scrotal skin in that it is essentially
spaces within the penis are continuous with the hairless and well supplied with sebaceous and sweat
veins responsible for drainage. The corpus spongio- glands. It functions to contain and protect the
sum originates at the pelvis as the bulb of the penis non-erect penis. The external part of the prepuce,
and distally surrounds the penile urethra within a or sheath, begins at the scrotum and has a distinct
groove on the ventral side of the penis. It contin- raphe, which is continuous with the scrotal raphae.
ues distally over the free end of the penis to form This external layer extends some distance cranially
the glans penis (corpus spongiosum glandis). This before reflecting dorsocaudad to the abdominal wall
is responsible for the distinct bell shape of the stal- to form the preputial orifice. The internal layer of
lion’s penis that is seen during full erection. The the prepuce extends caudad from the orifice to line
urethral process is distinctly visible at the centre of the internal side of the sheath, then reflects craniad

2.125

Dorsal process
of glans

Outer layer of Inner layer of
preputial fold preputial fold Glans penis Blood vessels lying
between deep and
superficial layers of fascia

Tunica albuginae of
penis surrounding only
corpus cavernosum penis
Corpus spongiosum penis
Preputial ring Free part of Urethral Urethra
the penis process Bulbospongiosus muscle

Fig. 2.125 Schematic diagram of the erect penis and prepuce of a horse (left) and a cross-section of the free
part of the penis (right).