MUSCLES OF THE TRUNK. 269 



1. Iliac Fascia, oe Lumbo-iliac Aponeurosis (Fig. 165, a). 



This is a very resisting fibrous expansion, covering the great psoas and iliacus 

 muscles. Attached, inwardly, to the tendon of the small psoas, outwardly to 

 the angle and external border of the ilium, this aponeurosis, as it extends for- 

 •wards over the great psoas, degenerates into connective tissue. Behind, it also 

 becomes attenuated in accompanymg the two muscles it covers, until near their 

 insertion into the internal trochanter of the femur. Its external or inferior face 

 receives, posteriorly, the insertion of the crural arch, and gives attachment to 

 the long adductor of the leg ; for the remainder of its extent, it is covered by 

 the peritoneum. 



2. Great Psoas Muscle (Psoas Magnus) (Fig. 165, 1). 



i&j/nonj/ms.— Sublumbo-troclian t : n eus— Gi'rard. Psoas — Bourgelat. {Lumho-femoral — Leyh.) 



Form — Situation. — This is a loug muscle, flattened above and below at its 

 anterior extremity, prismatic in its middle, and terminated in a cone at its 

 posterior extremity. It lies beneath the transverse processes of the lumbar 

 vertebrae. 



Structure. — Almost entirely fleshy, this muscle is formed of very delicate 

 fasciculi, which are directed backwards, and long in proportion to their super- 

 ficial and deep situation. They all converge to a tendon which is enveloped by 

 the iliacus, and is confounded with it. 



Attachments. — It is attached : 1. By the anterior extremity of its fleshy 

 fasciculi to the bodies of the last two dorsal and the lumbar vertebrae, except the 

 hindermost, and to the inferior face of the two last ribs and the transverse 

 processes of the lumbar vertebrae. 2. By its posterior tendon to the internal 

 trochanter, in common with the iliacus. 



Relations. — Below, with the pleura, the superior border of the diaphragm, 

 and the lumbo-iliac aponeurosis, which separates it from the peritoneum and the 

 abdominal viscera situated in the sublumbar region ; above, with the two last 

 internal intercostals, the quadratus lumborum, and the intertransversales muscles ; 

 inwardly with the small psoas and the internal branch of the iliacus ; outwardly, 

 for its posterior third, with the principal branch of the latter muscle. 



Action. — A flexor and rotator of the thigh outwards when its fixed point is 

 the loins, this muscle also flexes the lumbar region when the thigh is a fixed 

 point. It is, therefore, one of the agents which determine the arching of the 

 loins, and which operate, during exaggerated rearing or prancing, in bringing 

 the animal into a quadrupedal position again. 



3. Iliac Psoas Muscle (Iliacus) (Fig. 165, 3). 



Synonyms.— T\\o-irochaxiixnevii&—Girard. (Leyh divides this muscle into two portions, 

 which he describes as the great and middle ilio-femoralis. 



Form — Situation — Direction. — This is a very strong, thick, and prismatic 

 muscle, incompletely divided into two unequal portions by the groove for the 

 reception of the tendon of the great psoas : an external portion, somewhat con- 

 siderable in size ; and an internal, small. These two muscular portions lie at 

 the entrance to the pelvis, on the inner face of the ilium, in an oblique direction 

 downwards, backwards, and inwards. 



Structure. — It is almost entirely fleshy. The fasciculi forming it are spread 



