218 



MUSCLES OF THE ABDOMEN. 



Fig. us.* arch thrown from the tendon 



of one cms to that of the other, 

 beneath which pass the aorta, 

 the right vena azygos, and 

 thoracic duct. The great 

 splanchnic nerves pass through 

 openings in the lesser muscle 

 on each side, and the lesser 

 splanchnic nerves through the 

 fibres which arise from the 

 ligamentum arcuatum inter- 

 num. 



Relations. By its superior 

 surface with the pleura, the 

 pericardium, the heart, and 

 the lungs. By its inferior 

 surface with the peritoneum; 

 on the left with the stomach 

 and spleen ; on the right with 



the convexity of the liver ; and behind with the kidneys, the supra-renal 

 capsules, the duodenum, and the solar plexus. By its circumference with 

 the ribs and intercostal muscles, and with the vertebral column. 



Actions. The external oblique muscle, acting singly, would draw the 

 thorax towards the pelvis, and twist the body to the opposite side. Both 

 muscles, acting together, would flex the thorax directly on the pelvis. 

 The internal oblique of one side draws the chest downwards and outwards: 

 both together bend it directly forwards. Either transversalis muscle, act- 

 ing singly, will diminish the size of the abdomen on its own side, and both 

 together will constrict the entire cylinder of the cavity. The recti muscles, 

 assisted by the pyramidales, flex the thorax upon the chest, and, through 

 the medium of the lineaB transversse, are enabled to act when their sheath 

 is curved inwards by the action of the transversales. The pyramidales 

 are tensors of the linea alba. The abdominal are expiratory muscles, and 

 the chief agents of expulsion ; by their action the foetus is expelled from 

 the uterus, the urine from the bladder, the faeces from the rectum, the bile 

 from the gall-bladder, the ingesta from the stomach and bowels in vomit- 

 ing, and the mucous and irritating substances from the bronchial tubes, 



* The under or abdominal side of the diaphragm. 1, 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, wnich is closed only by the serous membranes of the abdomen and chest. 

 5. The ligamentum arcuatum externum 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 mus- 

 cular fasciculus from this tendon curves to the left side of the greater muscle between 

 the oesophageal 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 ossophageal 

 opening ; in this figure the CESophageal opening is tendinous at its anterior part, a struc- 

 ture which is not uncommon. 13. The opening for the inferior vena cava, in the ten- 

 dinous centre of tli3 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 beneath the ligamentum 

 arcuatum facternum , this muscle has also been removed on the left side. 



