218 MUSCLES OF THE ABDOMEN. 



wall of the sheath terminates in a thin curved margin, the apo- 

 neuroses of the three muscles passing altogether in front of the 

 rectus. 



The next two muscles can be examined only when the viscera of 

 the abdomen are removed. To see the quadratus lumborum, it is 

 also necessary to divide and draw aside the psoas muscle and the an- 

 terior lamella of the aponeurosis of the transversalis. 



The QUADRATUS LUMBORUM muscle is concealed from view by 

 the anterior lamella of the aponeurosis of the transversalis muscle, 

 which is inserted into the bases of the transverse processes of the 

 lumbar vertebrae. When this lamella is divided, the muscle will be 

 seen arising from the last rib, and from the transverse processes of the 

 four upper lumbar vertebrae. It is inserted into the crest of the ilium 

 and ilio-lumbar ligament. If the muscle be cut across or removed, 

 the middle lamella of the transversalis will be seen attached to the 

 apices of the transverse processes ; the quadratus being enclosed be- 

 tween the two lamellae as in a sheath. 



Relations. Enclosed in the sheath formed by the transversalis 

 muscle, it is in relation in front, with the kidney, the colon, the 

 psoas magnus, and the diaphragm. Behind, but also separated by its 

 sheath, with the erector spinae. 



The PSOAS PARVUS arises from the tendinous arches and interverte- 

 bral substance of the last dorsal and first lumbar vertebra, and termi- 

 nates in a long slender tendon which expands inferiorly and is inserted 

 into the ilio-pectineal line and eminence. The tendon is continuous by 

 its outer border with the iliac fascia. 



Relations. It rests upon the psoas magnus, and is covered in by 

 the peritoneum ; superiorly it passes beneath the ligamentum arcu- 

 atum of the diaphragm. It is occasionally wanting. 



DIAPHRAGM. To obtain a good view of this important inspiratory 

 muscle, the peritoneum should be dissected from its under surface. It 

 is the muscular septum between the thorax and abdomen, and is com- 

 posed of two portions, a greater and a lesser muscle. The greater 

 muscle arises from the ensiform cartilage ; from the inner surfaces of 

 the six inferior ribs, indigitating with the transversalis ; and from the 

 ligamentum arcuatum externum and internum. From these points, 

 which form the internal circumference of the trunk, the fibres converge 

 and are inserted into the central tendon. 



The ligamentum arcuatum externum is the tipper border of the an- 

 terior lamella of the aponeurosis of the transversalis : it arches across 

 the origin of the quadratus lumborum muscle, and is attached by one 

 extremity to the base of the transverse process of the first lumbar 

 vertebra, and by the other to the apex and lower margin of the last 

 rib. 



The ligamentum arcuatum internum^ or proprium, is a tendinous 

 arch thrown across the psoas magnus muscle as it emerges from the 

 chest. It is attached by one extremity to the base of the transverse 

 process of the first lumbar vertebra, and by the other is continuous 



