82 THE VOYAGE OF H.M.S. CHALLENGER. 



Relations. — The muscle is deeply situated at its origin, lying between the external 

 oblique and the aponeurotic origin of the inner portion of the rectus abdominis. 

 Above the origin of the latter it is subcutaneous, and rests upon the pectoralis major. 



Nerve supi)ly. — A twig from the nerve which supplies the pectoralis major. 



Remarks. — This muscle is described by Schoepss as forming a portion of the pectoralis 

 major. From Gervais and Alix it has received the name which for want of a better I have 

 adopted. 



3. Pectoralis mediiis. 



Pectoral moyen, Vicq d'Azyr, 1772, p. 624, No. 2. 



Pectoral moyen, Cuvier, 1805, torn. i. p. 277. 



Described by Merrem, p. 152, No. 2. 



Der Heine BmstmHskel, Wiedemann, p. 83. 



Der Mcine oder mittlere Brusfmuslcel, Tiedemann, p. 306, No. 2. 



Der kleine Bi-ustmuslcel, Heusinger, p. 183, No. 2. 



Le second pectoral, Meckel, vol. vi. p. 36, No. 11. 



Der grimte Oherarmheber, Schoepss, p. 124, No. 21. 



Pectoralis minor, Reid, p. 141. 



Suhclaviiw, Eolleston, p. 624. 



Subclavius, Selenka, Bd. vi. p. 118, No. 44. 



Moyen pectoral, Gervais and Alix, 1878, p. 24. 



Attachments. — The pectoralis medius arises from the whole of the anterior surface of 

 the sternum, as well as from the entire length of the keel of that bone, with the 

 exception only of those points which afford attachment to the pectoralis major. It 

 moreover takes a considerable attachment to the sterno-clavicular membrane. From 

 these origins the fibres converge to a stout tendon, which, after passing through the 

 foramen triosseum as through a pulley, is inserted into an oblique ridge situated on the 

 outer surface of the shaft of the humerus close to the head of that bone. The ridge in 

 question separates the head of the bone from the shaft. 



Action. — Passing as it does over the pulley formed by the bones of the shoulder 

 girdle, this muscle acts as the great extensor of the wing at the shoulder joint. In other 

 words, it raises the wing, and hence by some authors has been named the levator humeri. 



Relations. — Superficially the muscle is covered by the pectoralis major. From 

 above its outer border, close to the shoulder joint, the pectoralis minor passes forwards 

 to its insertion. 



Nerve supply. — A branch from the nerve which supplies the pectoralis major. 



Variations. — In Aptenodytes longirostris, in addition to the above, the muscle has 

 an extensive origin from the anterior surface of the proximal half of the coracoid bone. 



Remarks. — The pectoralis medius, as was well known to Schoej)ss and Gervais, shows 

 a distinct indication of a separation into two parts, the anterior half of the muscle, which 

 arises chiefly from the sterno-clavicular membrane, being separated by a cellular interval 



