244 



MUSCLES OF THE THORAX. 



of the right usually lying anterior to those of the left, and, curving upwards, 

 limit an opening for the transmission of the oesophagus, before ending in 

 the central aponeurosis. 



-g- Fig. 195. THE LOWER HALF OF 



=>' THE THORAX, WITH FOUR LUM- 



BAR VERTEBRAE, OPENED so AS 



TO SHOW THE DIAPHRAGM 



FROM BEFORE (modified from 

 Luschka). 



a, sixth dorsal vertebra ; b, 

 fourth lumbar vertebra ; c, ensi- 

 form process of the sternum ; d, 

 the aorta descending in front of 

 the lower dorsal vertebras ; d', the 

 aorta emerging in the abdomen 

 below the arch formed by the 

 meeting of the pillars of the dia- 

 phragm ; e, the oesophagus de- 

 scending through its aperture in 

 the diaphragm ; /, opening in the 

 tendon of the diaphragm for the 

 inferior vena cava ; 1, central, 2, 

 right, and 3, left division of the 

 trefoil tendon of the diaphragm ; 

 4, right, and 5, left muscular part, 

 descending from the margins of the 

 tendon to be attached to the ribs ; 

 6, the right, and 7, the left crus 

 or pillar of the muscle ; 8, to 8', 

 in the three upper intercostal spaces 

 of the right side the internal 

 layer of intercostal muscles inter- 

 rupted towards the vertebral co- 

 lumn, where in the two upper 

 spaces the external layer, 9, 9, is 

 seen ; in the lowest space shown 



the external layer is not represented ; 10, 10, on the left side, indicate the form and 

 position of a part of the subcostal or innermost layer of intercostal muscles. 



6. The lie/amentum 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 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 ligamenta arcnata diaphragmatic muscular fibres take their origin, and 

 are directed upwards to the posterior part of the tendinous centre. 



c. The fibres arising from the cartilages of the six lower ribs form a series 

 of serrated slips interdigitating with the attachments of the transversalis 

 abdomiuis muscle. They sometimes arise also in part from the osseous 

 ribs. The fibres proceeding from the eusiform cartilage form a narrow slip, 

 sometimes divided, on each side of which there occurs an interval, in 

 which the lining membranes of the thorax and abdomen are separated 

 only by a small quantity of loose connective tissue. The anterior fibres of 

 the diaphragm are much the shortest. The fibres of the sternal and costal 

 slips, after being united into the general plane of the muscle, rise in an 



