THE LIMBS OF THE HORSE 113 



long and short dorsal sacro-iliac ligaments, and the gluteal fascia. 

 Several tendinous strata occur in the substance of the muscle, the 

 strongest of these being attached to the gluteal line of the ilium, thus 

 dividing the muscle into superficial and deep portions. 



The insertion of the middle gluteal is double : (1) The greater 

 (superficial) part is inserted to the highest and most posterior part of 

 the great trochanter of the femur. (2) The deeper part ends in a stout, 

 flattened tendon that plays over the convex, anterior portion of the 

 great trochanter, and is attached to a special ridge immediately distal 

 to the convexity. The trochanteric bursa (bursa trochanterica) inter- 

 venes between the tendon and the bone. According to some authorities, 

 the deeper part of the middle gluteal muscle should be regarded as a 

 separate m. glutceus accessorius. 



M. PIRIFORMIS. — The piriformis^ muscle lies along the posterior 

 border of the middle gluteal, with which it is so blended as to lead the 

 dissector to regard the two muscles as one, unless warned to the 

 contrary. 



The origin of the piriformis (inseparably blended with the middle 

 gluteal muscle) is from the edge of the sacrum, and its insertion is to 

 the inter- trochanteric crest of the femur. 



Dissection. — The whole of the middle gluteal muscle, except its 

 insertion, must now be removed. This must be done with care, other- 

 wise there is danger that the underlying deep gluteal muscle may be 

 injured. The removal of the middle gluteal permits the dissector to 

 determine that its deeper portion {m. ghckeus accessorius) is attached to 

 the gluteal line of the ilium and to that area of the bone that is lateral 

 to the line. Examination of the trochanteric bursa also is now possible. 



M. GLUTEUS PROFUNDUS. — The short but strong deep gluteal muscle 

 arises from the rough lateral surface of the sciatic spine, a portion of 

 the adjacent surface of the ilium, and a narrow area of the sacro-spinous 

 ligament where this is attached to the sciatic spine, and is inserted into 

 the margin of the convex portion of the great trochanter. As will be 

 seen later, some of its fibres are connected with the capsule of the 

 hip joint. 



Mm. gemelli. — Though generally named in the plural, there is some 

 justification for regarding the gemelli^ of the horse as constituting 

 a single muscle, divisible into two strata except along its cranial border. 

 Both strata arise from the lateral border of the ischium opposite the 

 lesser sciatic foramen. The superficial stratum is inserted into the 

 trochanteric fossa close to the insertion of the internal obturator 

 muscle. The more extensive deep stratum is inserted within the inter- 



' Piruia [L.], a pear. Forma [L.], shape. 

 2 Gemellus [L.], twin. 



