152 The TJwrax 



not oblique, and that the zone of anaesthesia in fracture of the spine is 

 horizontal. 



The diaphragm, an important muscle of inspiration, arises from the 

 back of the xiphoid, the inner surfaces of the lower six ribs (where it 

 interdigitates with the transversalis), and, posteriorly, from the arcuate 

 ligaments. It also arises by two pointed crura, of which the right 

 descends rather lower than the left, namely, to the fourth lumbar 

 vertebra. 



Roughly, the attachment of the phrenic plane may be marked by 

 a line extending obliquely round the trunk from base of the xiphoid 

 cartilage to the last rib. 



According to Sibson, the central tendon descends about an inch 

 during inspiration, and with it descend the superjacent, and attached, 

 pericardium, the heart, and the base of the lungs. Sometimes, in 

 an anaemic subject, with the descent of the heart and the ascent of 

 the chest-wall during inspiration, the subclavian artery becomes so 

 stretched over the edge of the first rib that a bruit is heard there, the 

 radial pulse being lost at the very end of inspiration. That the bruit 

 is not the result of subclavian aneurysm is proved by causing the 

 patient to cease breathing after expiration, when the murmur disap- 

 pears and the radial pulse returns. 



The openings in the diapliragiu are the osseo-aponeurotic notch in 

 front of the twelfth dorsal vertebra for the aorta, vena azygos major, 

 thoracic duct, and left sympathetic ; a tendinous one between the 

 right and central leaflets for the vena cava ; and a third, a$ oval one, 

 for the oesophagus and the vagi : this is muscular, being formed by 

 the decussation of the inner fibres of the crura. 



Just on the outer side of the xiphoid there is an irregular gap in 

 the diaphragmatic fibres through which the superior epigastric artery 

 descends and some hepatic lymphatics mount to the mediastinal 

 glands. By this space also a diaphragmatic hernia may escape, and 

 through it the subperitoneal connective tissue joins that of the anterior 

 mediastinum. Along this loose tissue an anterior mediastinal abscess 

 may find its way into the epigastric region. 



Because of the upward extension of the abdominal cavity within the 

 circle of the ribs, the liver, stomach, spleen, and kidneys might almost 

 be counted as thoracic viscera. In fracture of the lower ribs the pleura 

 and lung, as well as the peritoneum, liver, spleen, and kidney, may be 

 lacerated by broken bone. 



Paralysis of the diaphragm embarrasses all the expulsive efforts, 

 and leaves respiration and vocalisation to be carried on almost entirely 

 by the intercostals. 



In healthy inspiration the ribs ascend and the diaphragm is de- 

 pressed, the abdominal viscera being pushed downwards and forwards ; 

 but, the diaphragm being paralysed, when the patient takes a breath 

 the ribs ascend as usual, but the abdominal muscles, taking advantage 



