284 FASCIA AND MUSCLES OF THE HORSE 



Structure. — The ischio-pubic head Ues on the pelvic floor and covers the ob- 

 turator foramen. It is thin and fan-shaped. The ihac head extends along the 

 lateral wall of the pelvis, and is pennate, with a central tendon throughout. Both 

 terminate on a flat tendon which passes outward through the lesser sciatic fora- 

 men to be inserted into the trochanteric fossa. A synovial bursa facilitates the 

 play of the tendon over the external border of the ischium.^ 



Relations. — The pelvic surface is covered by the pelvic fascia and the perito- 

 neum. The obturator vessels and nerve lie between the two heads, and the internal 

 pudic vessels and nerve lie along the dorsal edge of the iliac head. 



Blood-supply. — Obturator and internal pudic arteries. 



Nerve-supply. — -Great sciatic nerve. 



4. Gemellus'' (Fig. 455). — This is a thin, triangular muscle, which extends 

 from the external border of the .ischium to the trochanteric fossa. 



Origin. — The external border of the ischium near the ischiatic spine. 



Insertion. — The trochanteric fossa. 



Action. — To rotate the femur outward. 



Structure. — Fleshy, some fibers being inserted into the tendon of the obturator 

 internus. 



Relations. — Dorsally, the tendon of the obturator internus and the gluteus 

 profundus; ventrally, the obturator externus. 



Blood-supply. — Obturator artery. 



Nerve-supply. — Sciatic nerve. 



III. ANTERIOR MUSCLES OF THE THIGH 



This group consists of the sartorius, quadriceps femoris, and capsularis. 



1. Sartorius. — This is described on p. 281. 



2. Quadriceps femoris (Figs. 179, 186, 200) (Crural triceps). — This con- 

 stitutes the large muscular mass which covers the front and sides of the femur. It 

 has four heads, one of which, the rectus, arises from the ilium; the other three 

 arise from the femur. All are inserted into the patella. 



(1) Rectus femoris. — This is fusiform and rounded. It arises by two tendons. 



Origin. — Two depressions on the shaft of the ilium above and in front of the 

 acetabulum. 



- Insertion. — The base and anterior surface of the patella. 



Action. — ^To extend the stifle joint and to flex the hip joint. 



Structure. — It has two short strong tendons of origin; beneath the outer one 

 is a bursa. The belly is rounded and rests in a groove formed by the other portions 

 of the cjuadriceps. Its sides are covered by a strong tendinous layer which fur- 

 nishes insertion to fibers of the vasti. The tendon of insertion is formed by the 

 fusion of these tendinous layers on the lower part of the muscle. The lower portion 

 of the muscle is pennate, the fibers on either side converging on the tendon at an 

 acute angle. 



Relations. — Internally, the iliacus, sartorius, and vastus internus; externally, 

 the tensor fasciae latse, glutei, and vastus externus; posteriorly, the hip joint and 

 the vastus intermedins; anteriorly, the fascia lata and the skin. The anterior 



^ The iliac head is described by some authors as a separate muscle, and termed tlie pyri- 

 formis. This does not seem desirable, especially since it is at least probable that the honio- 

 logue of the pyriformis of man is that portion of the middle gluteus which is inserted into the 

 back of the trochanteric ridge. 



2 The name is based on the arrangement in man, in whom the muscle consists of two 

 fasciculi forming a groove between them for the tendon of the ol)turator internus. In the horse 

 it is untlivided, and is grooved for the obturator tendon, so that at first sight it appears to be 

 double. The gemellus may be regarded as the extrapelvic head of the obturator internus 

 (Gegenbaur) . 



