THORACIC WALL 3 



wards, posteriorly, and medially to the vertebral column. In 

 the first part of its extent it is formed by the cartilages of the 

 seventh, eighth, ninth, tenth and eleventh ribs, and in the 

 second part by the lower border of the twelfth rib. 



The lower margin of the thorax gives attachment to the 

 diaphragm, a highly vaulted or dome-shaped musculo-tendinous 

 partition, which intervenes between the cavity of the thorax 

 above and that of the abdomen below. It forms a convex 

 floor for the thorax, and a concave roof for the abdomen. 

 By its upward projection it greatly diminishes the general 

 vertical depth of the thoracic cavity. 



But the diaphragm does not form an unbroken partition. 

 It presents three large openings, by means of which structures 

 pass to and from the thorax, viz. (i) for the aorta, thoracic 

 duct, and vena azygos ; (2) for the oesophagus and vagi 

 nerves ; (3) for the inferior vena cava. Besides these there 

 are other smaller apertures which will be mentioned later. 



THORACIC WALL. 



Two days at least should be devoted to the dissection of 

 the thoracic wall. 



In addition to the osseous and cartilaginous framework, 

 the walls of the chest are built up partly by muscles, and! 

 partly by membranes, and in connection with these there are 

 numerous nerves and blood-vessels. 



( External intercostals. 

 Muscles, . J Internal intercostals. 



j Transversi thoracis. 



i^Subcostals. 



[ Anterior intercostal membranes. 

 Membranes, . . -j Posterior intercostal membranes. 



[Pleural membrane (parietal part). 



? Intercostal nerves. 



Nerves and Arteries J Aorti S ^costal arteries. 



Superior intercostal arteries. 



l,Internal mammary arteries. 



Dissection.- Portions of certain of the muscles of the upper limb and 

 of the abdominal wall are still attached to the thoracic wall on each 

 side. Antero- posteriorly the dissector will meet with the pectoralis major, 

 the pectoralis minor, and the serratus anterior, whilst towards the lower 

 margin of the chest he will recognise the rectus abdominis anteriorly, 

 and the obliquus externus and latissimus dor si upon its lateral aspect. The 

 rounded tendon of the sttbclavius may also be seen taking origin from 

 the first costal arch. These remnants must be removed so as to lay 

 bare the costal arches and the intercostal muscles. In detaching the 

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