_ 718^ 



— It is, however, suggestive to note the variety of connection which 

 it may have with the pectorahs major. It may be (1) superficial to 

 that muscle which presents a gap in its fibres (Abraham and others), 

 (2) superficial to that muscle which possesses a marked thinning at 

 that point (WmoLE, case 2). This is the intermediate stage between 

 1 and (3) where it is superficial to the pectoralis muscle which pre- 

 sents no obvious loss of substance (the ordinary adult form). Again 

 (4) one portion may be superficial and another deeper than the pec- 

 toralis major (Abraham) or (5) it may j)ierce that muscle (Turner^): 

 „In the specimen in which the muscle arose from the ö*** and 6"^ costal 

 cartilage and the osseous part of the G*'' rib, it pierced the great pec- 

 toral muscle on its way to the surface"). These facts are strong 

 confirmatory evidence of the theory that the sternahs is due to a rota- 

 tion of the fibres of the great pectoral. It should next be noted that 

 the part of the great pectoral which is rotated is generally the same. 

 I have endeavoured to show in a paper now in the press, „on the 

 Pectoral Group of Muscles", that the group consists of three radial 

 factors, which may exhibit a secondary lamination into deeper and more 

 superficial parts, and that each of these sectors has its own nerve. 

 These are (1) manubrial or claviculo-manubrial supplied by external 

 anterior thoracic nerve; (2) gladiolar supplied by internal anterior 

 thoracic ; (3) abdominal supplied by lateral thoracic. This last is ge- 

 nerally absent in Man but may be represented by pectoralis quartus 

 or some of the forms of Achselbogen. Now in the great majority of 

 cases it is some portion of the middle or gladiolar sector which is 

 rotated and as Cunningham has shown it is nearly always from the 

 internal anterior thoracic nerve or the loop between it and the ex- 

 ternal that the muscle receives its supply which is just what 

 might have been expected from the nerve-supply of the pectoral muscle. 

 In those cases where the muscle receives its supply from the external 

 anterior thoracic nerve, the facts may be explained by the rotation of 

 a part of the anterior sector or which I think more likely by the well 

 known varying amount of intercommunication in the loop between the 

 anterior thoracic nerves. In two cases, however, (3 and 4 of this note) 

 I have seen the muscle arising from the anterior abdominal wall. Here 

 we have, I think, to do with a rotation of the fibres of the third or ab- 

 dominal sector. I regret that I did not secure the nerve in these 

 cases, but it would probably have been derived from the internal an- 



1) Journal of Anatomy and Physiology, vol. 1, p. 246. 



