576 



GENITAL ORGANS OP THE STALLION 



(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 arter}^ 



(5) The ductus deferens. 



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

 muscular tissue about the vessels. 



(7) The visceral layer of the timica 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 Avhich 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 mesorohium, 

 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 VAGENALIS 



The tunica vaginalis is a flask -like serous sac which extends through the in- 

 guinal canal to the bottom of the scrotum. 



Spermatic vessels and nerves 



Like the abdominal peritoneum, of 

 which it is an evagination, it con- 

 sists of two layers — parietal and vis- 

 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 

 fold analogous to the mesenterj' of 

 the intestine. The visceral layer 



or tunica vaginalis propria covers the spermatic cord, testicle, and epididjmiis. 

 The external cremaster muscle (AI. 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 vaginahs opens into the 

 general peritoneal sac is distinguished by the name vaginal ring. It is four or five inches (ca. 

 10 to 12 cm.) from the linea alba, and two or three inches (oa. 6 to 8 cm.) in front of the Uio-peo- 

 tineal eminence. In stalhons it will usually admit the end of the finger readily, but it may be 



Parietal layer 

 of iunicii- 

 vaginalis 



Mesorchium 



Cremaster 

 internus 



Ductus 

 deferens 



Fig. 516. — Diagram of Cross-section of Spermatic Cord 

 AxD Tunica Vaginalis; Latter Hepresented as Dis- 

 tended. 



