2tii THE ANATOMY OP THE HORSE. 



2. The Dartos. If a portion of skin be removed from the scrotum, it 

 will expose a reddish-yellow layer, composed of connective-tissue with 

 many elastic fibres and a considerable quantity of involuntary muscular 

 tissue. This is the dartos, and, like the remaining tunics of the 

 testicle, it forms two distinct pouches, one for each testicle. In the mesial 

 plane, over the median raphe, the right and left pouches are applied 

 together and form the septum scroti; but superiorly they separate to 

 allow the penis to pass between them. Traced upwards, the dartos is 

 continuous around the external abdominal ring Avith the subcutaneous 

 fascia. Under the contraction of the muscular tissue of the dartos, the 

 scrotum becomes firm and wrinkled; during relaxation the scrotum is 

 smooth and pendulous. 



3. The Spermatic Fascia, continuous with the tendon of the external 

 oblique tendon. 



4. The Cremasteric Fascia, continuous with the internal oblique 

 muscle. 



5. The Infundibuliform Fascia, continuous with the transversalis 

 fascia. 



6. The Tunica Vaginalis Reflexa, a layer of serous membrane con- 

 tinuous with the peritoneum of the abdominal cavity. 



In Plate 37 these layers are semi-diagrammatically represented as suc- 

 ceeding each other like the coats of an onion. The dissector will probably 

 be unable to discriminate layers 3, 4, and 5. The tunica vaginalis reflexa, 

 he will recognise as a semitransparent layer which, when cut through, 

 takes him into a smoothly lined pouch in which the testicle lies free. 

 This is the sac of the tunica vaginalis, a diverticulum of the peritoneal 

 cavity. 



In the foetus the testicles make their first appearance in the sub- 

 lumbar region, close behind the kidneys. As development proceeds, 

 they descend through the abdominal wall into the scrotiuu ; and hence 

 the correspondence between the coverings of the testicle and the layers 

 that compose the wall of the abdomen. 



If the dissector will now lay hold of the testicle, and endeavour to 

 drag it out of the opening which he has made in its coverings, he will 

 bring into view the spermatic cord. The testicle, he will observe, is 

 covered by a glistening serous membrane, the tunica vaginalis propria, 

 which he can trace upwards on the cord. This spermatic cord contains 

 the vessels, nerves, and excretoiy duct (vas deferens) of the testicle, 

 Avhich structures descend through the abdominal wall by an oblique 

 passage termed the inguinal canal. In the upper part of this canal, 

 which is not to be exposed at present, the tunica vaginalis propria of the 

 cord is continuous with the tunica vaginalis reflexa. 



The Cremaster Muscle is continuous with the cremasteric fascia 

 already described. It is a bright red muscle, placed in the cord beneath 



