320 FASCIA AND MUSCLES OF THE HORSE 



Blood-supply. — Lumbar and circumflex iliac arteries. 

 Nerve-supply. — Lumbar and femoral nerves. 



3. Iliacus. — This muscle covers the ventral surface of the ilium lateral to the 

 sacro-iliac articulation, and extends beyond the lateral border of the bone, under- 

 neath the middle gluteus. 



Origin. — The ventral surface of the ilium lateral to the ilio-pectineal line, the 

 ventral sacro-iliac ligament, the wing of the sacrum, and the tendon of the psoas 

 minor. 



Insertion. — The trochanter minor of the femur, by a common tendon with 

 the psoas major. 



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 medial and lateral parts. 

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

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

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

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

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

 major in front of the hip joint. 



Relations. — Dorsally, 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 

 level of the hip joint the chief relations are: medially, the femoral vessels, the fem- 

 oral nerve, and the sartorius muscle; laterally, the rectus femoris and tensor fasciae 

 latee; 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 lateral part of the ven- 

 tral 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 TOng of the sacrum 'and the ventral 

 sacro-iliac ligament. 



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

 acting singly, to produce lal^pral flexion of the loins. 



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

 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 thoracic and first three 

 lumbar 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. — (See p. 279.) 



n. THE LATERAL MUSCLES OF THE HIP AJNTD THIGH 



Under this head the muscles of the lateral surface of the pelvis and thigh, and 

 those which form the posterior contour of the latter, will be described. 



1. Tensor fasciae latae (Fig. 267).— This is the most anterior muscle of the 

 superficial layer. It is triangular in form, with its apex at the tuber coxae. 



Origin. — The tuber coxae. 



Insertion. — The fascia lata and thus indirectly to the patella, the lateral patel- 

 lar ligament, and the crest of the tibia. 



