116 OF THE MUSCLES. 



posterior of the upper head of the tibia. Insertion. Into 

 the capsular ligament ; and by tendon into the outer con- 

 dyle of the femur. 



Action. To guard the capsular ligament ; and to rotate the 

 femur. 



LuMBRici. A pair of these poorly developed muscles 

 belong to each leg ; and are the only muscles below the knee 

 or hock. Their pale fleshy heads are not always found ; 

 but when they are present they terminate in long tendons, 

 which run to the pad at the back of the fetlock, 



MUSCLES OF THE ANUS. 



Sphinctor ani {Plate III. 2). Encircles the opening to 

 the anus ; and enters within it for the depth of four or five 

 inches. It has neither origin nor insertion. Action. To close 

 the anus ; it being a very bad symptom when, during disease, 

 this muscle relaxes. 



Retractor ani inferior. Bijid posteriorly. Origin. Os 

 innominata, above the origin of the gluteus internus. In- 

 sertion. Into the rectum ; both heads mingling with the 

 fibres of the sphinctor ani, upon the lower surface. Action. 

 To retract the anus ; puUing it downwards, after the passage 

 of the dung. 



Retractor ani superior. Origin. From the inferior of 

 the sacrum. Insertion. Mingles with fibres of the sphinctor 

 ani, upon their upper surface. Action. To co-operate with 

 the inferior retractor ; pulling the anus upwards. 



Levator ani consists of two slips of red muscular fibres. 



muscles of the tail {Plate III. 4). 



Compressor coccygis. This muscle can be divided into 

 three distinct layers. Origin. From the superior border of 

 the OS innominata. Insertion. Into the inferior of the first 

 coccygeal bone ; and into the next three bones of the tail. 



Besides this, the tail is generally described as consisting 

 of four muscles : a levator, which elevates the tail ; a pair 

 of curvators, which turns the tail to either side ; and a de- 

 pressor, which lowers the tail. But the firmness with which 

 the tail can be held down by the horse is owing to the de- 

 pressor, assisted by the compressor and other muscles. 



The four muscles of the tail originate in a tendinous 



