21-6 OUTLI>ES OF EQUINE ANATOMY. 



of tlie serous membrane covering the floor of tlie belly 

 through the inguinal canal. The external surface of this 

 membrane is sroooth, covered with tessellated epithelium, 

 which secretes a serous fluid to enable the surface of tunica 

 vaginalis testis or reflexa to glide on it freely. These two 

 serous layers are posteriorly connected by d^frcenimi, which 

 extends up as far as the loins whence the testes originally 

 descended. In the fcetal colt, as in adult birds, the testis 

 occupies a position against the kidney. To its under part 

 is attached a white fibrous cord, gubernaculum testis, sur- 

 rounded by serous membranes, running to the internal 

 abdominal ring. In the process of development this guides 

 the testis towards the inguinal canal, and then becoming 

 everted in passing into the scrotum, its serous covering 

 becomes the tunica vaginalis scroti. The testis may 

 generally be found in the scrotum at birth ; it subse- 

 quently, at a period varying according to the breed and 

 treatment of the colt, passes again into the inguinal canal, 

 where it remains for some time, sometimes permanently, 

 and again descends into the scrotum. Sometimes, how- 

 ever, it is drawn up into the abdomen, and on account of 

 increase of its size is unable again to descend. If this 

 occurs to but one testis, the animal is termed a monorcJiid or 

 rig, and if the other testis has been removed by castration, 

 he will be lustful, but an uncertain stock-getter. 



The immediate coats of the testis are a serous layer, 

 tunica vaginalis testis and tunica alhuginea. The latter is a 

 dense fibrous mass, forming the stroma of the organ, send- 

 ing fibres and septa inwards from an outer layer, to support 

 and separate the different lobules of the gland, and to in- 

 vest its larger vessels. It predominates at the upper part 

 of the organ, where it is termed mediastinum testis. The 

 testis consists of a number of long tubules curled uj)on 

 themselves, forming the lohuli testis. Each lobule is iso- 

 lated from its fellows, receives a vascular coating (by some 

 anatomists termed tunica vasculosa), and terminates Supe- 

 riorly in a vas rectum. The vasa recta unite and form a 

 plexus in the substance of mediastinum testis, at the 

 anterior part of which they converge to form the vasa 

 effereiitia, which emerge from the testis proper, and, be- 

 coming very convoluted, (coni vasculosi), form the j^os^mor 

 globus of the ejndidymis. 



The testicle, thus constituted, is a rounded body, clon- 



