MYOLOGY 207 



arises from the tuberosity of the ischium only, as in the 

 human species. In the pig, it also takes origin higher up 

 from the sacro-sciatic ligament and the coccygeal aponeu- 

 rosis. In the horse, it extends still further, for it is also 

 attached to the crest of the sacrum. 



The indication of these origins is of importance from the 

 point of view of external form, and to convince ourselves of 

 this it is sufficient to compare, in the ox and the horse, the 

 region of the pelvis situated below the root of the tail. In 

 the ox, whose semi-tendinosus arises from the tuberosity 

 of the ischium only, this region is depressed, and the cavity 

 which is formed at this level is limited behind by the tuber- 

 osity, which we know is very thick and prominent above. 

 This causes' the superior part of the crupper to be less 

 oblique than in the horse. This characteristic is more 

 especially marked in the cow, the bull having this region of 

 a more rounded form. 



In the horse, on account of the semi-tendinosus ascending 

 to the coccyx, and even to the sacrum, the depression in 

 question does not exist, and the presence of the tuberosity 

 of the ischium is only slightly revealed. 



Descending from the origin indicated above, and inclining 

 more and more inwards, the semi-tendinosus proceeds to 

 blend with the aponeurosis of the leg, to be inserted into 

 the anterior border of the tibia, after crossing over the 

 internal surface of the latter. It forms the internal boun- 

 dary of the popliteal space. 



When this muscle contracts, taking its fixed point at the 

 pelvis, it flexes the leg. If, on the other hand, it takes its 

 fixed point at the tibia, it makes the pelvis describe a see- 

 saw movement, and acts accordingly in the movement of 

 rearing. 



It is sometimes named the ' internal or tibial flexor of the 

 leg,' in opposition to the crural biceps, which, as stated above, 

 is then the external flexor of the same region. 



Semi-membranosus (Fig. 68, 32 ; Fig. 87, 2 ; Fig. 88, 2). 

 — This muscle, situated on the inner side of the semi-ten- 

 dinosus, can be seen only when the thigh is regarded on 

 its posterior aspect. 



