852 THE GENERA TI VE APPA RA TVS. 



1. Tunica Vaginalis. 



The tunica vaginalis, in the domesticated animals, is only a diverticulum 



of the abdominal cavity, the serous membrane of which the peritoneum 



becomes a hernia in the inguinal canal, passing through the upper (internal) 

 inguinal ring, and prolonged below the inferior (external) ring, so as to 

 form a serous sac, which is enveloped by membranous walls. 



We have to study, in the vaginal sheath: 1, Its interior; 2, The 

 enveloping membranes which form the external walls, and to which we give 

 the common name of scrotum. 



Interior. The serous sac constituting the tunica vaginalis, is vertically 

 elongated, and slightly inclined downwards, inwards, and backwards. Its 

 inferior extremity, forming the bottom, or cul-de-sac, is pear-shaped, and 

 lodges the testicle and its epididymis. Its middle portion, contracted into a 

 narrow canal, contains the spermatic cord. The superior extremity, or 

 entrance, is open, to maintain communication with the abdominal cavity; 

 through it pass the spermatic vessels and vas deferens. 



As has been said, the peritoneum forms the vaginal sac. As in the 

 abdomen, it is divisible into two layers parietal and visceral. The latter 

 (tunica vaginalis propria) covers the testicle and the cord ; while the former 

 (tunica vaginalis communis, or reflexa) lines the innermost of the membranous 

 coverings which serve as a wall to the tunica vaginalis. These two layers 

 are made continuous by a serous fraenum, analogous to the mesentery which 

 sustains the floating colon ; like it, it is formed by the junction of the two 

 layers. Flat, elongated from above to below, and extending vertically from 

 one end of the sheath to the other, this frsBnum is attached, by its upper 

 border, behind the spermatic cord; its lower extremity passes over the 

 epididymis, and from it on to the testicle ; above, it is continued into the 

 abdominal cavity, in accompanying the different canals composing the cord. 



(A small quantity of serous fluid is usually present in the tunica 

 vaginalis. When in excess it gives rise to hydrocele.) 



ENVELOPING MEMBRANES. The stratified layers that form the external 

 walls of the vaginal sheath, and which are generally described in anatomical 

 treatises, with the two serous layers, as the envelopes of the testicle, are four 

 in number. Reckoning them from within to without, they are the fibrous 

 tunic, cremaster muscle, dartos, and scrotum. 



FIBROUS TUNIC (infundibuliform fascia). This forms the most complete 

 covering to the tunica vaginalis, extending, as it does, over the whole surface 

 of the parietal serous layer, to which it is closely adherent. Very thin, 

 especially at the points corresponding to the cremaster, this membrane is 

 continuous, around the upper inguinal ring, with the transversalis fascia, of 

 which it is only a dependency ; its external face is in relation with the 

 cremaster and dartos. 



CREMASTER. This muscle is usually described as an envelope of the 

 testicle, by the name of tunica eryfhroides. In the domesticated animals, it 

 is a bright-red band, attached, above, to the inner or peritoneal surface of 

 the ilio-lumbar aponeurosis; it descends into the inguinal canal, envelops 

 outwardly only the middle portion of the sheath of the testicle, and expands 

 below on the cul-de-sac, where its fibres terminate by small tendons, which 

 are inserted into the external surface of the fibrous tunic. Therefore it is 

 that the envelope the cremaster forms is very incomplete, the greater portion 

 of the testicle, and the inner side of the cord, being left unprotected by this 

 muscular tunic. It is in relation, inwardly, with the fibrous membrane, to 



