REPORT ON THE SPHENISCID.^. 81 



its long axis which, combined with the backward stroke, gives rise to the screw-like 

 motion of the organ observable when the bird is progressing through the water. 



Relations. — The anterior fibres of the great pectoral muscle extend across the clavicle 

 to the middle line of the body, and are only separated from those of the opposite side 

 by a tendinous raphe, to which both are attached. The external border of the muscle is 

 free. Upon its cutaneous surface lies the " muscle des parures." 



Nerve supply- — A special branch from the large cord of the brachial plexus. 



Variations. — In Eudijptes clinjsocome from the Falkland Islands, the attachment 

 of the pectoralis major to the sterno-clavicular membrane is more limited than in 

 Eudyptes chrysocome from Tristan d'Acunha. In Eudyptes chrysocome from Kerguelen the 

 greater pectoral muscle does not take any attachment to the sterno-clavicular aponeurosis. 

 In Aptenodytes longirostris the origin of the muscle from the postero-external angle of 

 the sternum is much more extensive than in Eudyptes, and it extends along the outer 

 margin of the sternum for the posterior half of that bone. 



Remarks. — Reid describes the muscle in Aptenodytes as arising from " the cartilages 

 of the ribs, and from the anterior part of the coracoid bone," in addition to the origins 

 above described. Such was not the case in the specimens examined by myself. 



Gervais and Alix describe the pectoralis major in Eudyptes chrysolophus as arising 

 from " the aponeurosis of the great oblique, which separates it from the sterno-costal 

 articulations," in addition to the attachments above described. This description is not 

 borne out by my own dissections. 



2. Muscle des parures. 



Der Brusthaut-niuskel, Tiedemann, vol. i. p. 134. 



Dermo-humeralis, Owen, p. 24. 



Panniculus carnosus (second portion), Eeid, p. 139. 



Attachments. — The muscle so named by Gervais and Alix is flat and riband-like, and 

 has a somewhat peculiar disposition. Arising by means of a strong fascia, which covers 

 the external oblique muscle of the abdomen from the free cartilaginous extremity of the 

 pubic bone, it passes forwards and inwards to the posterior margin of the sternum. Here 

 it is reinforced by a number of fibres from the subcutaneous tissue covering the knee- 

 joint, and thereafter diverging from its fellow of the opposite side, passes forwards parallel 

 to the outer border of the pectoralis major, along with the posterior fibres of which muscle 

 it is inserted into the anterior margin of the humerus. 



Action. — This muscle co-operates with the external fibres of the pectoralis major in 

 depressing the wing. It would appear, moreover, that its posterior fibres, that is, those 

 which form the subcutaneus abdominalis above described (p. 55), wiU co-operate with the 

 muscles of the abdominal wall in their various actions. 



(ZOOL. CHALL. EXP. PART XVIIl. — 1883.) S 11 



