REPORT ON THE SPHENISCID^. 83 



from the posterior or sternal portion. This separation is more distinct in Spheniscus 

 demersus than in any other sjaecies. The same arrangement, according to Gervais, 

 obtains in the Gallinacese and Tinamidse. The enormous size of the pectoralis medius 

 in comparison with that of the pectoralis major in the Penguins has been noted by every 

 anatomist who has dissected any member of the group. 



4. Pectoralis minor. 



Le petit pectoral, Vicq d'Azyr, 1772, p. 625, Xo. 3. 

 Le petit pectoral, Cuvier, 1805, vol. i. p. 278, Xo. 3. 

 Described by Merrem, p. 152, No. 3. 

 Der kleinste Brustmuskel, Wiedemaun, p. 83. 

 Der kleinste Bnistmuskel, Tiedemann, p. 307, No. 3. 

 Pectoralis minimus, Heusiuger, p. 103, Xo. 3. 

 Troisihne pectoral, Meckel, vol. vi. p. 38, No. 12. 

 Der drittc Brustmuskel, Sohoepss, p. 113, Xo. 16. 

 Coraco-bracldalis, Reid, p. 141. 

 Coraco-hraehialis longus, Selenka, p. 114, Xo. 40. 

 Coraco-hrachial, Gervais and Alix, p. 23. 



Attachments. — The pectoralis minor arises from about half an inch of the lateral 

 margin of the sternum, just posterior to the coraco-stemal articulation, as well as, but to 

 a greater extent, from an aponeurotic septum between the pectoralis medius and minor, 

 which septum is attached to the external margin of the shaft of the coracoid bone. 

 The fibres form an oval belly, from which a tendon passes forwards and upwards, to be 

 inserted into the outer margin of the tricipital fossa of the humerus, close to the posterior 

 margin of the tendon of insertion of the pectoi*alis medius. 



Action. — This muscle depresses the wing at the shoulder joint, so as to approximate 

 it to the side of the body. The muscle, therefore, comes into play in producing the 

 effective or propulsive stroke of the wing. Moreover, in consequence of the passage of its 

 tendon upwards below the neck of the humerus, the muscle is enabled to rotate the 

 entire wing around the axis of the humerus in such a manner as to direct the concavity 

 of the wing forwards and downwards. In this respect the pectoralis minor is the 

 antagonist of the pectoralis major, which rotates the wing in the opposite direction. 

 These two muscles are the principal agents in bringing about the screw-like motions of 

 the wing at the shoulder joint, which are observable in the living bii'd. 



Relations. — The muscle is concealed by the pectoralis major, and lies in contact with 

 the outer border of the pectoralis medius. Its upper surface rests against the axillary 

 vessels and nerves as they pass out of the thorax. 



Nerve supjily. — A twig from the nerve which supplies the pectoralis major. 



Remarks. — Selenka is of opinion that this muscle, named by him the coraco- 

 brachialis longus, is identical with muscle No. 17 of Schoepss. This does not appear to 



