INTERCOSTAL NERVES. 489 



Upji.')' .siV n'.-rves. At first the nerves lie between the pleura and Course of 

 the external intercostal muscle with an artery and vein ; but they u PP ersix > 

 soon enter between the intercostal muscles, and extend forwards to 

 the side of the sternum (p. 439). In their course they supply 

 to the muscles of the thoracic wall, as well as to the 



levatores costariuu and serrati muscles of the back, and cutaneous 

 offsets to the surface, which are described in the dissection of 

 the upper limb (p. 13). 



There are some deviations in the first and second nerves from the Exceptions 

 arrangement above specified. w0 ' 



The first nerve ascends in front of the neck of the first rib, First nerve 

 and enters the brachial plexus. Before it leaves the chest it 

 supplies to the first intercostal space a branch, which furnishes 

 muscular offsets, and becomes cutaneous by the side of the sternum. 

 There is not any lateral cutaneous offset from this branch, except 

 when the second nerve is not as large as usual. 



The second nerve may extend a considerable way on the wall of Second 

 the chest before entering between the intercostal muscles ; and it 

 frequently sends upwards a branch to join the first nerve. It is 

 remarkable in having a very large lateral cutaneous branch, which 

 we have seen described in the upper limb as the intercosto-humeral 

 nerve. In front it ends like the others. 



The lower five nerves resemble the foregoing in their course and ^ wer five 



nerves. 



branches in the intercostal spaces : their termination in the 

 abdominal wall is described on p. 274. 



UPPER SURFACE OF THE DIAPHRAGM. The centre of the muscle Upper sur- 

 is tendinous, and the circumference is fleshy. In contact with the diaphragm. 

 upper surface are the lung with the pleura on each side, and the 

 heart and pericardium in the middle : the phrenic vessels and Parts touch- 

 nerves pierce this surface, external to the pericardium. In the lng ' 

 diaphragm are the following apertures ; one for the oesophagus Apertures 

 and the pneumo-gastric nerves, a second for the vena cava, a third * 

 for the aorta with the thoracic duct and the large azygos vein, and 

 a cleft on each side for the splanchnic nerves. Beneath it the 

 sympathetic passes into the abdomen. 



SECTION III. 



LIGAMENTS OF THE TRUNK. 



The ligaments of the vertebrae, ribs, and sternum are now to be Articula- 

 exainined. ttonaoflhe 



ARTICULATIONS OF THE RIBS. Each rib is united to the spinal 

 column at the one end, and to the costal cartilage at the other. 

 Between it and the spine there are two synovial joints, and two 

 sets of ligaments, viz., one between the head of the rib and the 

 bodies of the vertebra, and a second passing from the neck and 

 tuberosity to the transverse processes of the vertebrae. 



