576 GENITAL ORGANS OF THE STALLION 
(2) The spermatic veins, which form the pampiniform plexus around the 
artery. 
(3) The lymphatics, which accompany the veins. 
) Sympathetic nerves, which run with the artery. 
(5) The ductus deferens. 
) The internal cremaster muscle, which consists of bundles of unstriped 
muscular tissue about the vessels. 
(7) The visceral layer of the tunica vaginalis. 
The first four of these constituents are gathered into a rounded mass which 
forms the anterior part of the cord; they are united by connective tissue, inter- 
spersed with which are bundles of the cremaster internus. The ductus deferens is 
situated postero-medially, enclosed in a special fold detached from the medial surface 
of the tunic; hence it is not visible laterally. 
The term spermatic cord is to a certain extent misleading as applied to most animals, while 
in man the structure is distinctly cord-like. In the horse, when the tunica vaginalis is slit open 
and the “cord”’ stretched out, the latter is seen to have the form of a wide sheet, the mesorchium, 
which has a thick, rounded anterior edge, the so-called ‘‘ vascular part” of the cord. The posterior 
edge of the mesorchium is continuous with the parietal layer of the tunic; its medial surface pre- 
sents posteriorly the deferential fold (Plica ductus deferentis). Between the two layers of the 
mesorchium are bundles of unstriped muscle (cremaster internus) and small vessels. 
THE TUNICA VAGINALIS 
The tunica vaginalis is a flask-like serous sac which extends through the in- 
guinal canal to the bottom of the scrotum. Like the abdominal peritoneum, of 
which it is an evagination, it con- 
Spermatic vessels and nerves sists of two layers—parietal and vis- 
HN ceral. The parietal layer or tunica 
vaginalis communis lines the scrotum 
below; its narrow, tubular part lies 
in the inguinal canal, and is directly 
continuous with the parietal perito- 
neum of the abdomen at the abdom- 
inal inguinal ring. The cavity of the 
tunica vaginalis (Cavum vaginale) is 
a diverticulum of the general perito- 
neal cavity, with which it communi- 
cates through the vaginal ring (An- 
nulus vaginalis); it contains nor- 
mally a small quantity of serous fluid. 
The parietal layer is reflected from 
the posterior wall of the inguinal 
canal around the structures of the 
cord, forming the mesorchium, a 
Parietal layer 
of tunica 
vaginalis 
Mesorchium - 
Cremaster _| 
internus 
Ductus _ 
deferens 
BCTION OF SPERMATIC CorD 
Fria. 516.—D1aGraM or Cross-s 
AND Tunica VAGINALIS; LATTER REPRESENTED As D1s- 
TENDED. 
the intestine. The visceral layer 
or tunica vaginalis propria covers the spermatic cord, testicle, and epididymis. 
The external cremaster muscle (M. cremaster externus) lies on the lateral and 
posterior part of the tunic, to the scrotal part of which it is attached. 
Confusion has arisen from the use of the term abdominal or internal inguinal ring in two 
senses. The term is used to designate the abdominal opening of the inguinal canal, but it is also 
often applied to the opening of the cavity of the tunica vaginalis. It should not be used in the 
latter sense. The peritoneal ring at which the cavity of the tunica vaginalis opens into the 
general peritoneal sac is distinguished by the name vaginal ring. It is four or five inches (ca. 
10 to 12 em.) from the linea alba, and two or three inches (ca. 6 to 8 cm.) in front of the ilio-pee- 
tineal eminence. In stallions it will usually admit the end of the finger readily, but it may be 
fold analogous to the mesentery of | 
