436 



THE MUSCULATURE 



the ilio-hypogastric, inguinal and genito-femoral nerves as these course forward between this 

 muscle and the internal oblique. 



Action. — The chief function is to compress the abdominal viscera. Through the portions 

 extending between the lower margins of the thorax on each side it serves to contract the thorax 

 and so may aid in expiration. 



Relations. — It lies on the inner side of the lower ribs, the internal oblique and rectus muscles, 

 and is covered on the deep surface by the transversalis fascia. 



Variations. — It is verj' rarely absent. It shows considerable variation in the extent of its 

 development. The pubo-peritonealis is a similar muscle which may pass from the pubic crest 

 to the transversus near the umbilicus. The pubo -transversalis is a small muscle which may 

 extend from the superior ramus of the pubis to the transversalis fascia near the abdominal 

 inguinal ring. The tensor laminae posterioris vaginae musculi recti abdominis, essentially like 

 the preceding, maj' extend from the inguinal ligament to the rectus sheath on the deep surface 

 of the rectus muscle near the umbilicus. The tensor laminae posterioris vaginae musculi 

 recti et fasciae transversalis abdominis likewise extends from the transversalis fascia near the 

 abdominal inguinal ring to the fold of Douglas. 



C. Lumbar Muscle 



The quadratus lumborum (fig. 406). — Origin. — From — (1) the internallip of the iliac crest 

 near the junction of the middle and dorsal thirds, and the iliolumbar ligament; (2) the transverse 

 processes of the three or four lower lumbar vertebrae; and (3) the lumbo-dorsal fascia. 



Fig. 391. — Diaphragm. 



Opening for vena 

 cava inferior 



Right division of 

 tendon 



Aorta 



Right crus 

 Psoas minor 



Psoas major . . 



Transversus \ \\ 



abdominis 



Quadratus 

 lumborum 



Sternal origin 



Middle division 

 of tendon 



— <E sophagus 



i Left division 



{^ \ of tendon 

 Costal origin 



Medial lumbo- 

 costal arch 



- \—\— Left crus 



// "/ Lateral lumbo- 

 costal arch 

 Transverse pro- 

 cess of second 

 lumbar vertebra 

 Fourth lumbar 

 vertebra 



Structure and insertion. — From the origins there arises a complex quadrangular muscle 

 belly from which spring the fasiculi of termination. These extend to — (1) the transverse 

 processes of the upper three or four lumbar vertebne; (2) to the fibre-bands which extend out 

 laterally in the lumbar fascia from the transverse processes; and (3) to,the medial pa rt of the 

 lower border of the twelfth rib. " ' 



Nerve-supply. — Through direct branches from the first three or four lumbar nerves. 



Action. — It serves primarily to produce lateral flexion of the spinal column. When both 

 muscles act together, they produce extension of the column. The muscle also serves to depress 

 and fix the twelfth rib. 



Relations. — It rests posteriorly on the lumbo-dorsal fascia and the transverse processes of 

 the lumbar vertebra;. Its medial edge is partly covered by the psoas. In front of it also lie 

 the kidney, the intestines, and the lumbar arteries and nerves. It is ensheathed by membranes 

 continued over each surface from the transversalis fascia. Of these, the anterior is the better 

 marked and is called the lumbar fascia. 



Variations. — There is much individual variation in the internal structure of the muscle and 

 in its attachments. — Its in.sertion may extend to the eleventh rib."*- 



The psoas major and minor belong essentially to the musculature of the lower limb and are 

 there described (p. 455). ^ 



D. The DiAPHRAGii^r V^^i 



The diaphragm (figs. 386, 391). — This dome-shaped musculo-membranous sheet has, when 

 seen from above, something of the outline of a kidney. It consists of a pair of muscles which 

 arise one on each side from the thoracic wall and are inserted into a central tendon. Lateral 



