iyo ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 253. — The sternum, sternal ends of the clavicles and the ribs, with the intercostales, and the 



transversus thoracis, seen from behind. 

 Fig. 254. — The fifth to the twelfth thoracic vertebras and the vertebral extremities of the corresponding 



ribs, with the intercostales and subcostales, seen from in front. 

 On the left side the intercostal ligaments have been removed. 



iliocostalis), and are divided into the levatores costarum breves and longi. The levatores costarum 

 breves (Fig. 243) arise from the transverse processes of the seventh cervical to the eleventh thoracic 

 vertebrae and insert into the rib next below- between the tubercle and the angle. The levatores 

 costarum longi (Fig. 243) are found chiefly on the lower ribs and are distinguished from the 

 breves in that they pass over one rib and insert into the second below near its costal angle. The 

 levatores costarum become markedly broader toward their insertion and usually possess aponeu- 

 roses. 



The subcostales (Fig. 254) are flat muscles which are not always present and vary greatly 

 in their development. From the direction of their fibers they are to be grouped with the internal 

 intercostal muscles, with the posterior portion of which they are continuous. They are found 

 chiefly in the lower thoracic region and bridge over one or two ribs. They are usually partly 

 tendinous both at their origin and at their insertion. 



The transversus thoracis {triangularis sterni) (Fig. 253) is a very thin flat muscle, the 

 greater portion of which is tendinous, which arises by a broad aponeurosis from the posterior 

 surfaces of the body and xiphoid process of the sternum and inserts by short broad tendinous 

 slips into the inner surfaces of the cartilages of the second or third to the sixth ribs. The muscle 

 is constant but very variable in its development. 



All the muscles of the intercostal series are supplied by the intercostal nerves which pass, together -with the vasa 

 intercostalia, between the internal and the external intercostal muscles. 



The intercostal muscles are important muscles of respiration. The great majority of them are muscles of inspiration, 

 but the transversus thoracis and the subcostales probably play some part in expiration. 



THE PECTORAL FASCIA. 



The pectoral fascia lies upon the pectoralis major and the lower portion of the serratus ante- 

 rior. The coracoclavicular fascia (costocoracoid membrane) is a much more pronounced layer which 

 is situated beneath the pectoralis major and upon the pectoralis minor, covering the subclavius 

 and the axillary vessels. It is particularly firm where it lies upon the subclavius and inserts into 

 the lower surface of the clavicle. Internally it is inserted into the upper costal cartilages; exter- 

 nally it is continuous with the axillary fascia. 



[As was the case in the dorsal region, all the muscles referred to the thoracic region in the above description do 

 not strictly belong to the thoracic musculature, but belong in part to the musculature of the upper extremity. This is 

 true with regard to the muscles of the first three layers, only those described as the muscles of the thoracic walls being 

 trunk muscles. 



These may be classified similarly to the abdominal muscles, but owing to the presence of a sternum in the thoracic 

 region and to the lessened mobility of the thoracic portion of the spinal column due to the presence of fully developed 

 ribs, no representatives of either the rectus or hyposkeletal groups occur in this region. The classification is consequently 

 as follows: 



