STERNAL GROUP. 197 



PECTORALIS PARVUS. 



(Sterno-prescapularis. ) 



(Fig. 75. g.) 



In front of the magnus, on tbe ant ero -inferior part of the 

 thorax, elongated and prismatic in form, its fibres extend out- 

 wards, forwards, and upwards ; it is lendinous at its origin, fleshy 

 elsewhere. 



Origin. — From the three or four anterior sternal segments, 

 cartilages, ribs, and cariniform cartilage. 



Insertion. — To the fascia in front of the shoulder-joint, and 

 the anterior costa of the scapula, nearly as high up as the origin 

 of the antea-spinatus. 



Relation. — Externally with the magnus and transversus; 

 inferiorly with the transversus and anticus ; internally with the 

 first costal cartilages, intercostales, and transversalis costarum ; 

 anteriorly with the levator humeri. 



Action. — To draw the shoulder-joint backwards and down- 

 wards, assist the magnus, and tense the scapular fascia. 



Sternal Group. 



The muscles of this unimportant group are two in number — 



Lateralis sterni. 

 Triangularis sterni. 



LATERALIS STERNI. 



{C osto-sternalis.) 



Placed along the inferior border of the serratus magnus, its 

 fibres extend downwards and backwards. It is flat, thin, and 

 aponeurotic at its extremities. 



Origin. — From the outer surface of the first rib, passing over 

 the next two or three ribs, and becoming attached to the ster- 

 num at about the fourth segment. 



Relation. — Externally with the pectorals ; superiorly with the 

 serratus magnus ; posteriorly with the rectus abdominis ; inter- 

 nally with the ribs and intercostals. 



Action. — An auxiliary muscle of expiration. 



