286 THE ANATOMY OF THE HORSE. 



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 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 Cremasteb 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 nest 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 Inpundibuliform 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 transversalis fascia. 



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

 forms the innermost stratum of the scrotum. When it is out 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 animal with such an undescended 

 testicle is termed a cryptorchid or "rig." 



The Spbematic 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 

 vagituilis propr'ia, 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 



