MUSCLES OF THE ABDOMEN. 193 



rior lamella of the internal oblique and the aponeurosis of the trans- 

 versalis. At the commencement of the lower fourth, the posterior 

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

 roses of the three muscles passing altogether in front of the rectus. 



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

 the viscera 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, and ligamentum arcuatum externum. 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 vertebras. 

 It is inserted into the crest of the ilium. 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 between the two lamelke 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 

 the sheath, with the erector sptnas. 



The psoas parvus arises from the tendinous arches and interverte- 

 bral substance of the last dorsal and first lumbar vertebrae, and ter- 

 minates in a long slender tendon which is inserted into the pectineal 

 line of the os pubis. 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 

 composed 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 upper 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 extremity of the transverse process of the first lum- 

 bar 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 transverse pro- 



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