286 THE ANATOMY OF THE HORSE. 



tissue with many elastic fibres and a considerable quantity of in- 

 voluntary 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 with 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 Cremaster Muscle. This is one of the envelopes of the 

 testicle and spermatic cord, but it cannot at present be exposed in the 

 whole of its extent. It will be brought partly into view by reflecting 

 the entire scrotal skin and dartos from the outer side of the sac. It is 

 a bright red muscle which descends through the inguinal canal, where 

 it envelopes the next stratum. After its emergence from the canal its 

 fibres diverge to enter the scrotum, and become inserted into the outer 

 surface of the next layer. 



4. The Infundibuliform Fascia. This is a layer of white fibrous 

 connective-tissue, which is continued upwards as a tube around the 

 spermatic cord, becoming continuous at the internal abdominal ring 

 with the transveralis fascia. 



5. The Tunica Vaginalis Reflexa. This is a serous layer, and it 

 forms the innermost stratum of the scrotum. When it is cut through 

 the testicle is exposed, lying with its surfaces free in what is a potential 

 cavity — the sac of the tunica vaginalis. This sac is a diverticulum or 

 protrusion of the peritoneum, with which it is continuous, through the 

 inguinal canal, at the internal abdominal ring. The inner free surface 

 of the tunica vaginalis reflexa is exquisitely smooth, in virtue of a layer 

 of endothelium. 



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 scrotum ; but some- 

 times this descent is not effected, one or both testicles remaining in the 

 abdomen or in the inguinal canal. An aninal with such an undescended 

 testicle is termed a cryptorchid or "rig." 



The Spermatic Cord. 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 sper- 

 matic cord contains the vessels, nerves, and excretory duct (vas deferens) 

 of the testicle, which structures descend through the abdominal wall by 

 an oblique passage termed the inguinal canal. In the upper part of this 



