THE DIAPHRAGM. 



323 



The crura or pillars arise by tendinous fibres, intimately connected with the 

 anterior common ligament, from the upper three or four lumbar vertebrae and 

 the interposed discs on the right side, and from the first and second vertebrae 

 and adjoining discs on the left side. The tendinous portions of the crura are 

 continued higher internally than externally, and curving forwards and inwards join 

 in the middle line so as to form an arch over the front of the aorta ; while inferiorly 

 their inner margins frequently meet behind that vessel, which is thus enclosed in 

 an oval fibrous loop or ring. The muscular fibres of the crura, springing from the 

 tendons in thick bundles, diverge as they pass upwards to the coneava posterior 

 margin of the central aponeurosis. The innermost fibres of the two pillars decussate 

 in front of the aortic opening, and pass up on opposite sides of the oesophagus, for 



Fig. 290. THE DIAPHRAGM, FROM 

 BELOW. (Allen Thomson.) | 



The lower ribs and sternum are drawn 

 upwards so as to expose and stretch the 

 lower surface of the diaphragm, and the 

 four upper lumbar vertebrae have been 

 exposed by the removal of all the muscles 

 on the right side, and the dissection of the 

 psoas magnus and quadratus lumborum 

 on the left side, a, aorta, emerging from 

 between the pillars on the first lumbar 

 vertebra ; b, oesophagus, in its aperture 

 between the muscular fibres, represented 

 too far to the right ; c, aperture for the 

 inferior vena cava, situated at the place 

 of union of the middle and right divisions 

 of the trefoil tendon ; d, fourth lumbar 

 vertebra ; e, e, twelfth ribs ; f, f, eleventh 

 ribs ; 1, tendinous part of the right crus ; 

 2, the left ; 3, tendinous arch formed by 

 their union over the aorta, above which 

 the decussation of the muscular fibres is 

 seen ; 4, second decussation of muscular 

 fibres in front of the oesophageal opening ; 

 5, on the right side, the attachment of 

 the arched ligaments to the first and second 

 lumbar transverse processes ; from 5 to e, 

 external arched ligament ; +, is in the 

 hollow of the internal arched ligament 

 from which the psoas has been removed ; 

 5, on the left side, external arched liga- 

 ment ; 6, middle division of the trefoil 



tendon, from which in front pass the slips of attachment of the diaphragm to the ensiform process ; 

 7, left, and 8, right divisions of the trefoil tendon ; from the outer and anterior margins of these the 

 costal slips of the muscle are seen diverging, and from the posterior border of the tendon the slips of 

 origin proceeding from the arched ligaments and the tendinous arch of the crura ; 9, part of quadratus 

 lumborum ; 10, part of psoas magnus. 



which they thus bound an elongated aperture, meeting and again decussating to 

 some extent anteriorly as they join the tendon. In the first decussation the fasciculus 

 derived from the right crus usually passes in front of that from the left, which is 

 much smaller and not unfrequently is altogether wanting. 



The internal arched ligament (ligamentum arcuatum internum) is a fibrous band 

 which extends from the body to the transverse process of the first lumbar vertebra, 

 and sometimes also to that of the second, and arches over the upper part of the 

 psoas muscle. The external arched ligament (ligamentum arcuatum externum) 

 extends outwards from the transverse process of the first lumbar vertebra to the last 

 rib, arching over the front of the quadratus lumborum : it is the upper part of the 

 fascia covering that muscle, somewhat increased in thickness. From both arched 

 ligaments muscular fibres take origin, and are directed upwards to the lateral portion 



VOL. II. V 



