COSTAL EEGION. 193 



Relation. — Internally with the ribs, transversalis costarum, 

 and longissimus dorsi ; externally with the rhomboideus, serratus 

 magnus, and latissimus dorsi. 



Action. — Respiratory ; the anterior portion drawing the ribs 

 outwards and forwards, acts as an inspiratory, the posterior, by 

 drawing them backwards and upwards as an expiratory muscle. 



TEANSVERSALIS COSTAEUM. 



( Trachelo-costalis. ) 



(Pl. III. 13.) 



Situated on the supero-lateral part of the thorax, it is long, 

 thin, and semipenniform, the fibres passing downwards, outwards, 

 and forwards, its numerous muscular bundles each terminating 

 in a flat tendon. 



Origin. — From the transverse processes of the first lumbar 

 vertebrae, and the ribs near their tubercles. 



Insertion. — To the external surface of all the ribs, a tendon 

 to each, and one to the last cervical vertebra. 



Relation. — Externally with the preceding muscle ; internally 

 with the ribs ; superiorly with the longissimus dorsi. 



Action. — It compresses the ribs, assisting in expiration. 



LEVATORES COSTARUM. 

 ( Transverso-costales. ) 



Situated deeply on the back, these muscles are small, flat, and 

 triangular, extending obliquely dowuAvards and backwards. They 

 are fleshy and tendinous. 



Origin. — Superiorly, from the transverse processes of the 

 dorsal vertebrae, just above the tubercles of the ribs. 



Insertion. — Inferiorly to the external faces of the ribs, just 

 above their angles. 



Relation. — Externally with the longissimus dorsi ; internally 

 with the external intercostals, with which posteriorly they are 

 much blended. 



Action. — To raise and draw the ribs forwards, thus acting as 

 inspiratory muscles. 



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