344 MUSCLES OF THE ABDOMINAL CAVITY. 



into a plain towards the middle tendon, by which the cavity 

 of the thorax is enlarged, particularly at the sides, where the 

 lungs are chiefly situated ; and as the lungs must always be 

 contiguous to the inside of the thorax and upper side of the 



Fig. 89 * 



diaphragm, the air rushes into them, in order to fill up the 

 increased space. This muscle is assisted by the two rows of 



* The under or abdominal side of t*he diaphragm. J, 2, 3. The greater 

 muscle ; the figure 1 rests upon the central leaflet of the tendinous centre ; the 

 number 2 on the left or smallest leaflet ; and number 3 on the right leaflet. 4. 

 The thin fasciculus which arises from the ensiform cartilage ; a small triangular 

 space is left on either side of this fasciculus, which is closed only by the serous 

 membranes of the abdomen and chest. 5. The ligamentum arcuatum exiernum 

 of the left side. 6. The ligamentum arcuatum internum 7. A small arched 

 opening occasionally found, through which the lesser splanchnic nerve passes. 

 8. The right or larger tendon of the lesser muscle ; a muscular fasciculus from 

 this tendon curves to the left side of the greater muscle between the cesophagea! 

 and aortic openings. 9. The fourth lumbar vertebra. 10. The left or shorter 

 tendon of the lesser muscle. 11. The aortic opening occupied by the aorta, 

 which is cut short off. 12. A portion of the oesophagus issuing through the 

 cesophageal opening. 13. The opening for the inferior vena cava. in the tendi- 

 nous centre of the diaphragm. 14. The psoas magnus muscle passing beneath 

 the ligamentum arcuatum internum ; it has been removed on the opposite side 

 to show the arch more distinctly. 15. The quadratus lumborum passing be- 

 neath the ligamentum arcuatum externum ; this muscle has been removed on 

 the left side. 



