118 



OSTEOLOGY 



It' slopes downward and forward, so that the anterior part of the opening is on a 

 lower level than the posterior. Its antero-posterior diameter is about 5 cm., and 

 its transverse diameter about 10 cm. The lower opening is formed by the twelfth 

 thoracic vertebra behind, by the eleventh and twelfth ribs at the sides, and in front 

 by the cartilages of the tenth, ninth, eighth, and seventh ribs, which ascend on 

 either side and form an angle, the subcostal angle, into the apex of which the 



First thon 



Sternum 



Twelfth thoracic 



First lumbar 



FIG. 114. The thorax from the right. (Spalteholz.) 



xiphoid process projects. The lower opening is wider transversely than from 

 before backward, and slopes obliquely downward and backward, it is closed by 

 the diaphragm which forms the floor of the thorax. 



The thorax of the female differs from that of the male as follows: 1. Its capacity is less. 

 The sternum is shorter. 3. The upper margin of the sternum is on a level with the lower part 

 of the body of the third thoracic vertebra, whereas in the male it is on a level with the lower 

 part of the body of the second. 4. The upper ribs are more movable, and so allow a greater 

 enlargement of the upper part of the thorax. 



