276 FASCIA AND MUSCLES OF THE HORSE 



Action. — To flex the hip joint and to rotate the thigh outward. 



Structure. — The belly of the muscle is so deeply grooved for the psoas major 

 as to give the appearance of being completely divided into outer and inner portions. 

 When the psoas is removed, it is seen, however, that the two heads are not entirely 

 separated. The outer, larger head arises from the wing of the ilium chiefly; the 

 inner, smaller head arises chiefly from a small area on the shaft of the ilium, be- 

 tween the psoas tubercle and the depression for the inner tendon of the rectus 

 femoris, and from the tendon of the psoas minor. The two portions inclose 

 the psoas major in front of the hip joint. 



Relations.— Dorssdly, the ilium, sacrum, sacro-iliac articulation, the gluteus 

 medius, the ilio-lumbar and external circumflex vessels; ventrally, the iliac fascia, 

 inguinal ligament, the psoas major, sartorius, and abdominal muscles. At the 

 hip joint the chief relations are: internally, the femoral vessels, the femoral nerve, 

 and the sartorius muscle; externally, the rectus femoris and tensor fasciae latse; in 

 front, the abdominal muscles; behind, the hip joint. 



Blood-supply. — Lumbar, circumflex iliac, and deep femoral arteries. 



Nerve-supply. — Lumbar and femoral nerves. 



4. Quadratus lumborum. — This thin muscle lies on the outer part of the 

 ventral surfaces of the lumbar transverse processes. 



Origin. — The ventral surface of the upper part of the last two ribs and the 

 lumbar transverse processes. 



Insertion. — The ventral surface of the wing of the sacrum and the ventral 

 sacro-iliac ligament. 



Action. — Acting together, to fix the last two ribs and the lumbar vertebra?; 

 acting singly, to produce lateral flexion of the loins. 



Structure. — The muscle is pennate, and is curved with the convexity outward. 

 It is thin, largely mixed with tendinous fibers, and is, in general, little developed in 

 the horse in comparison with some of the other animals (e. g., dog, sheep). 



Relations. — Ventrally, the psoas major and the last intercostal and first three 

 lumliar nerves; dorsally, the last two ribs, the lumbar transverse processes, and 

 the lateral branches of the lumbar arteries. 



Blood-supply. — Lumbar arteries. 



Nerve-supply. — Lumbar nerves. 



5. Intertransversales lumborum (M. intertransversarii lumborum). — These 

 are described with the other spinal muscles. (See p. 238.) 



II. THE EXTERNAL MUSCLES OF THE HIP AND THIGH 



Under this head will be described the muscles of the outer surface of the pelvis 

 and thigh, and those which form the posterior contour of the latter. They are 

 given in the order in w^iich they may be conveniently examined. 



1. Tensor fasciae latae (Fig. 178). — This is the most anterior muscle of the 

 superficial layer. It is triangular in form, with its apex at the external angle of 

 the ilium. 



Origin. — The external angle of the ilium. 



Insertion. — The fascia lata, and thus indirectly to the patella, the external 

 straight ligament, and the crest of the tibia. 



Action. — To tense the fascia lata, flex the hip joint, and extend the 

 stifle joint. 



Structure. — The muscle arises by a rather small head, about two inches (ca. 

 5 cm.) wide, on the antero-inferior eminence of the external angle of the ilium. 

 Below this the belly spreads out and terminates about midway between the point 

 of the hip and the stifle in the aponeurosis. The belly fuses to a considerable ex- 

 tent with the superficial gluteus. The aponeurosis fuses with the fascia lata, and 



