574 GENITAL ORGANS OF THE STALLION 
part of the spermatic cord, and is very tortuous near the testicle; on reaching the 
attached border of the gland it passes backward in a flexuous manner, giving 
branches to the testicle and epididymis, turns around the posterior extremity, and 
runs forward on the free border to the anterior extremity. It is partially embedded 
in the tunica albuginea, and detaches lateral branches which ascend and descend in 
a tortuous fashion on each surface of the testicle; these give off small branches 
which enter the gland on the trabecule and septa. The veins on leaving the 
testicle, form a network, the pampiniform plexus, around the artery in the sper- 
matic cord. The spermatic vein, which issues from this plexus, usually joins the 
posterior vena cava on the right side, the left renal vein on the left side. The 
lymph-vessels follow in general the course of the veins and enter the lumbar lymph 
glands. The nerves, derived from the renal and posterior mesenteric plexuses, 
form the spermatic plexus around the vessels, to which they are chiefly distributed. 
THE SCROTUM 
The scrotum, in which the testicles and the adjacent parts of the spermatic 
cords are situated, is somewhat globular in form, but is commonly asymmetrical, 
since one testicle—more often the left—is the larger and more dependent. It 
varies in form and appearance in the same subject, according to the condition of its 
subcutaneous muscular tissue. The latter contracts on exposure to cold, so that 
the scrotum is drawn up and becomes thicker and wrinkled; when relaxed under the 
influence of heat or fatigue, or from debility, it becomes smooth and pendulous, 
with a constriction or neck superiorly. It consists of layers which correspond 
with those of the abdominal wall; considered from without inward, these are: 
(1) The skin, which is thin, elastic, usually dark or black in color, and smooth 
and oily to the touch. It presents scattered short fine hairs, and is abundantly 
supplied with very large sebaceous and sweat glands. It is marked centrally by ¢ 
longitudinal raphé scroti; this is continued forward on the prepuce and behind on 
the perineum. 
(2) The dartos (Tunica dartos) is reddish in color and is closely adherent to 
the skin except superiorly. It consists of fibro-elastic tissue and unstriped muscle. 
Along the raphé it forms a median partition, the septum scroti, wnich divides the 
scrotum into two pouches. Dorsally the septum divides into two layers which 
diverge on either side of the penis to join the abdominal tunic. At the bottom 
of the scrotum fibers connect the dartos closely with the tunica vaginalis (and thus 
indirectly with the tail of the epididymis), constituting the scrotal ligament.! 
Elsewhere the dartos is loosely connected with the underlying tunic by areolar 
tissue which contains no fat. 
(3) The scrotal fascia, which is apparently derived from the oblique abdom- 
inal muscles. 
It has been customary to describe three layers of fascia, in conformity with the accounts 
given in text-books of human anatomy. ‘These are: (1) The intercolumnar or spermatic fascia, 
derived from the margin of the external inguinal ring; (2) the cremasteric fascia, derived from the 
internal oblique muscle; (3) the infundibuliform fascia, derived from the fascia transversalis. 
The first two cannot be distinguished by dissection and the third is (in the serotum) fused with 
the parietal peritoneum of the tunica vaginalis. 
(4) The parietal layer of the tunica vaginalis.—This is a fibro-serous sac which 
is continuous with the parietal peritoneum of the abdomen at the internal inguinal 
ring. It is thin above, but is thick in its scrotal part, where it is strengthened by 
fibrous tissue (Lamina fibrosa) derived from the transversalis fascia. It will be 
described further under the caption tunica vaginalis.’ 
1 This is a remnant of the gubernaculum testis of the foetus. 
2 The tunica vaginalis is not a part of the scrotum in the strict or narrow sense of that term, 
but is included here on practical grounds. 
