2i8 Anatomy of the Rabbit. 



I. Muscles arising from the ventral surface of the posterior 

 thoracic and lumbar vertebrae and inserted on the pelvic girdle, 

 or on the lesser trochanter of the femur. These muscles are chiefly 

 distinguished by their vertebral position, on account of which and 

 the fixed condition of the pelvic girdle they combine the characters 

 of vertebral and appendicular muscles. 



(a) The psoas minor. Origin: Bodies of the four posterior 

 lumbar vertebrae. Insertion: Pecten of the pubis. The 

 flat, pointed tendon forms a square cross with a dorsal 

 (sacral) continuation of the inguinal' ligament, which is 

 stretched transversely from the mfddle of the inguinal liga- 

 ment to the centre of the body of the first sacral vertebra, 

 and on which the tendon is also inserted. 



It is necessary to divide the inguinal ligament and reflect its sacral 

 continuation, together with the tendon of the psoas minor. 



(b) The psoas major. Origin: Internal surfaces of the bases of 

 the last three ribs and bodies of the corresponding thoracic 

 vertebrae; also the lumbar vertebrae. Insertion: Lesser 

 trochanter. 



(c) The iliacus. Origin: Bodies of the last lumbar and first 

 sacral vertebrae, extending to the sacroiliac union. Inser- 

 tion: With the psoas major on the. lesser trochanter. The 

 two muscles together form the iliopsoas. 



The lumbar portion of the lumbosacral plexus, beginning with 

 the fourth lumbar nerve, lies on the ventral surface of the psoas major 

 and between the latter and the iliacus. The fifth lumbar is the chief 

 root of the femoral nerve (p. 225), the trunk of which may be traced 

 from a position between the two muscles distad over the dorsal surface 

 of the inguinal ligament to the medial surface of the thigh. The remain- 

 ing four nerves crossing the dorsal body-wall obliquely are the twelfth 

 thoracic and first three lumbar. 



The psoas major should be freed at its lateral margin and turned 

 toward the middle line, the fourth lumbar nerve being divided. 



(d) The quadratus lumborum. Origin: Bodies of the 

 posterior five thoracic vertebrae and the bases of the corres- 

 ponding five ribs; bodies and transverse processes of the 

 lumbar vertebrae. Insertion: Triangular processes of six 

 lumbar vertebrae and the posterior ventral angle of the iliac 

 wing, together with the adjacent portion of its medial sur- 

 face. 



