THE SPERMATIC CORD — THE TUNICA VAGINALIS 489 



vas deferens with the duct (or neck) of the corresponding vesicula seminalis; 

 they are thin-walled tubes, about 2 to 3 mm. long and 6 to 7 mm. wide, which 

 open into the urethra on either side of the colliculus seminalis. In about 15 per 

 cent, of subjects the vas deferens and duct of the seminal vesicle do not unite, but 

 open side by side into the urethra. From its origin until it reaches the dorsal 

 surface of the bladder the vas deferens has a uniform diameter of about a quarter 

 of an inch (ca. 6 mm.). It then forms a fusiform dilatation, the ampulla ductus 

 deferentis (Fig. 394); this part is about six to eight inches (ca. 15 to 20 cm.) long, 

 and in its largest part nearly an inch (ca. 2 cm.) in cUameter in the stallion; in 

 geldings the dilatation is usually not very pronounced. Beyond the ampulla the 

 duct abruptly contracts. 



Structure. — The wall of the vas deferens is thick and the lumen relatively 

 small, so that the tube has a firm and cord-like character. It is covered with peri- 

 toneum, except in the last few inches of its course. The loose adventitia contains 

 numerous vessels and nerves. The thick muscular coat consists of longitudinal 

 and circular layers. The mucous membrane has an epithelium of short columnar 

 cells. In the posterior part of the tube, and especiallj- in the ampulla, there are 

 numerous tubnlo-alveolar glands. 



Blood-supply. — Speruiatic and umbilical arteries. 



Nerve-supply. — Spermatic and pelvic plexuses. 



THE SPERMATIC CORD 



The spermatic cord (Funiculus .spermaticus) consists of the structures carried 

 down by the testicle in its migration through the inguinal canal from the abdominal 

 cavity to the scrotum. It begins at the internal inguinal ring, where its constituent 

 parts come together, extends obliciuely downward through the inguinal canal, 

 passes over the side of the penis, and ends at the attached border of the testicle. 

 It consists of the following structures: 



(1) The spermatic artery. 



(2) The spermatic veins, which form the pampiniform plexus around the 

 artery. 



(3) The lymphatics, which accompany the veins. 



(4) Sympathetic nerves, which run with the artery. 



(5) The vas deferens. 



(6) The internal cremaster muscle, which consists of bundles of unstriped 

 muscular tissue. 



■ (7) The visceral layer of the tunica vaginalis or mesorchium. 

 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 vas deferens is 

 situated posteriorly, inclosed in a special fold detached from the inner surface of 

 the mesorchium; hence it is not visible externally. 



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 inner 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 somewhat pjTiform serous sac which extends from the 

 internal inguinal ring through the inguinal canal to the bottom of the scrotum. 



