DISSECTION OF THE DOG 7 



Tunica vaginalis. — The tunica vaginalis is a serous membrane continuous, 

 through the inguinal canal, with the peritoneum. Like other serous membranes 

 it is composed of a parietal and a visceral part. The parietal portion lines 

 the interior of the scrotum and is. continuous with the visceral part in the 

 caudo-dorsal region of the scrotal cavity. The visceral part of the tunic will 

 be displayed after an examination of the testis and its surroundings has 

 been made. 



Dissection. — Cut through the parietal tunica vaginalis with a pair of scissors, 

 and examine the contents of the cavity of the scrotum. 



Testis et epididymis. — The testes are two oval organs, slightly flattened 

 laterally (especially on the medial surface), each lodged in its own compartment 

 of the scrotum. The long axis of each testis is oblique, and runs caudo-ventral. 

 The two surfaces, medial and lateral, are smooth and convex, as is also the 

 ventral border. The dorsal border and the two extremities are connected 

 with the epididymis. 



The epididymis of the dog is relatively large. It consists of an elongated, 

 laterally compressed mass formed by the tortuous windings of a long tube held 

 together by dense connective tissue and covered by the tunica vaginalis. 

 The body (corpus epididymidis), or main part of the structure, lies dorsal to 

 the testis. The cranial and caudal ends, known respectively as the head 

 (caput epididymidis) and the tail (cauda epididymidis), are adherent to the 

 extremities of the testis. The cauda is also firmly bound to the wall of the 

 scrotum. From the cauda the ductus deferens takes origin. The duct runs 

 cranialwards dorso-medial to the testis, at first somewhat convoluted but 

 afterwards straighter, and passes into the inguinal canal. 



Funiculus spermaticus. — The spermatic cord consists of the ductus 

 deferens and certain blood vessels, nerves, and lymphatics. The vein within 

 the cord is richly coiled and forms a prominent object, extending from the 

 head of the epididymis into the inguinal canal. Partly buried within the 

 venous mass is the internal spermatic artery (a. spermatica interna). 



The visceral part of the tunica vaginalis may now be followed. It is 

 applied closely to the testis and epididymis, and dips in between these two 

 organs, to form a cavity, the sinus epididymidis, the entrance to which is 

 lateral in position. Continued towards the inguinal canal, the tunic encloses 

 the spermatic cord, from which and from the epididymis it is reflected as a 

 mesentery containing fine nerve filaments. It will be observed that the 

 deferent duct and the external spermatic artery are enclosed in a special 

 sheath of the tunic which is an offset from the covering of the other 

 constituents of the spermatic cord. 



Pbjeputium. — The prepuce is a tubular sheath of integument enclosing the 

 glans of the penis, and, in the retracted state of this organ, circumscribing a 

 cavity which communicates with the surface by a slit-like orifice. The prepuce 



b 4 



