346 MUSCLES OF THE ABDOMINAL CAVITY. 



1. Quadratus Lumborum. 



Arises, somewhat broad, tendinous and fleshy, from the poste- 

 rior part of the spine of the os ilium. 



Inserted into the transverse processes of all the vertebrae of the 

 loins, into the last rib near the spine, and by a small tendon into 

 the side of the last vertebra of the back. 



Use. To move the loins to one side, pull down the last rib. 

 and, when both act, to bend the loins forwards. 



2. Psoas Parvus. 



Arises, fleshy, from the sides of the two upper vertebrae of 

 the loins, and sends off a small long tendon which ends thin and 

 flat, and is 



Inserted into the brim of the pelvis, at the junction of the os 

 ilium and pubis. 



Use. To assist the psoas magnus in bending the loins for- 

 wards ; and, in certain positions, to assist in raising the pelvis. 



N. B. This muscle is very often wanting. 



3. Psoas Magnus, 



Arises, fleshy, from the side of the body and transverse pro- 

 cess of the last vertebra of the back ; and, in the same manner, 

 from those of the loins, by as many distinct slips. At its 

 superior portion, this muscle is covered by a thin fibrous 

 expansion which is attached on the one hand to the points of 

 the transverse processes, and on the other to the bodies of the 

 upper lumbar vertebrae. This expansion, the arcus interior 

 of Senac and Haller (ligamentum arcuatum inter num), sepa- 

 rates the psoas from the diaphragm. On the outer side of 

 this is another aponeurotic arch, called ligamentum arcuatum 

 externum; it passes from the outer extremity of the former, 

 to the inferior margin of the last rib, embracing in its curve 

 below, the quadratus lumborum muscle. Both these arches 

 give origin on their upper margin to fibres of the lesser mus- 

 cle of the diaphragm, and serve to cut off more effectually 

 any communication between the thoracic and abdominal 

 cavities. 



