REPOFvT ON THE SPHENISCID^. 91 



Action. — The first and second heads of origin of the triceps co-operate with the 

 Latissimus dorsi in eftecting the backward or effective stroke of the wing. In conjunction 

 with the third and fourth heads, they are the principal extensors of the forearm at the 

 elbow joint. 



Relations. — The first head is to a large extent subcutaneous, and rests upon the 

 shoulder joint. The second head arises from the scapula close to the attachment of 

 the fibrous pulley of the latissimus dorsi. The tendon of insertion of the pectoralis 

 minor, as well as those of the latissimus dorsi, intervenes between the second and third 

 heads. 



Nerve supply. — The first and second heads are supplied by nerves derived from the 

 great cord of the brachial plexus. The third and fourth heads are supplied by branches 

 from the musculo-spiral nerve. 



Variations. — In Eudijptcs chrysolopjlius the second head of the triceps arises not only 

 from the axillary border of the scapula, but also from the fibrous pulley through which the 

 tendons of the latissimus dorsi pass. In this bird, moreover, the third and fourth heads 

 are quite continuous, and are not separated by an interval, as in the other species examined. 

 In Aptenodytes longirostris the external tendon of insertion of the triceps is inserted into 

 the ulna by two distinct slips, one of which coalesces with the internal tendon above 

 described. 



2. Brachialis intemus. 



Lc court flecJiisseur de Vavant Iras, Vicq d'Azyr, 1773, p. 572, Nu. 3. 



Ver EUenho(je7iheuger, Wiedemann, p. 89. 



Brachialis intemus, Tiedemann, p. 312, No. 2. 



Der innere Armmuskel, Heusinger, p. 184, No. 11. 



Le deiixieme flikhisseur de Vavant bras, Meckel, vol. vi. p. 4G, No. 2. 



Der kurze Beuger des Vorderarmes, Sohoepss, p. 141, No. 28. 



Brachialis intemus, Selenka, vol. vi. p. 1 25, No. 52. 



Court flechisseur de I'avant bras, Gervais and Alix, p. 27. 



Attachments. — The brachialis internus is a short quadrilateral muscle, which arises 

 from a slight depression occupying the lower third of the anterior (radial) margin of the 

 shaft of the humerus. The fibres pass in front of the humero-radial articulation, and are 

 inserted into a deep excavation on the anterior border of the radius, immediately below 

 the upper end of that bone. 



Action. — This muscle is the principal flexor of the forearm upon the humerus. 



Relations. — The brachialis internus rests upon the front of the elbow joint. 



Nerve supply. — A twig from the radial nerve, which is given off opposite the elbow 

 joint. 



Remarks. — According to Gervais and Alix, this muscle corresponds to the long 

 external supinator of the Crocodile. These authors consider that this muscle, because of 



