STERNAL GROUP. 197 



PECTORALIS PARVUS. 



(Sterno-prescapularis. ) 



(FiG. 75. g.) 



In front of the magnus, on the antero-inferior part of the 

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

 wards, forwards, and upwards ; it is tendinous 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; 

 interiorly 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. 



(Costo-sternalis.) 



Placed along the inferior border of the serratus magnus, ite 

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

 aponenrotic 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. 



