THE MUSCLES 69 



perhaps best to regard it as arising at about the level of the sternum. 

 The muscle passes forwards around the lateral parietes of the peri- 

 cardium, mesial to the thyroid gland, and between the hypobranchial 

 cartilages i and 2, passing ventral to the latter and dorsal to the 

 former. It is inserted on the dorsal side of the apex of the copula by 

 means of a strong tendon. The section of the muscle alongside the 

 pericardium passes through a sort of 'sleeve' of connective tissue, 

 so that its contraction does not affect the surrounding structures. 

 Within this 'sleeve', a short distance posterior to the os triangulare, 

 a small bundle of fibres separates from the main mass and loops 

 round mesialwards so to become attached to the antero-dorsal aspect 

 of the OS triangulare. This bundle was seen by v. Siebold as early as 

 1828, and was named by him M. hebosteoypsiloideus^ while it may 

 represent the muscle referred to by Carus as the oblique epischio- 

 hyoideum (9). 



Innervation : As in the superficial portion ; see above. 



Function : To retract the tongue or to depress the head, according 

 to circumstances. 



M. pectori-scapularis (Edgeworth) (m.p.s.). 



Schulterzungenbeinmuskel (omohyoideus) . . . Meckel (1828). 



Omo-hyoideus v. Siebold (1828); Rusconi (1854); Mivart (1869}; 



Humphry (1872); Hoffmann (1873-8); Osawa 



(1902). 



Scapulo-post-hyoidien ...... Duges (1834). 



Pectori-scapularis internus .... Fiirbringer (1873). 



Pectori-scapularis s. omo-hyoideus . Walter (1887); Druner (1901). 

 A small, relatively weak, spatulate muscle arising from the mesial 

 aspect of the ventral end of the scapula and inserted, as mentioned 

 above, at the lateral edge of the superficial portion of the M. rectus 

 cervicis at the level of the anterior inscriptio tendinea. 



Innervation: By a fine twig arising from the R. communicans 

 between the first and second spinal nerves. 



Function: The muscle acts as a brace to the M. rectus cervicis 

 superficialis. 



MUSCLES OF THE FORE-LIMB AND SHOULDER 

 I. Historical. 



The earliest author to make a special study of this region of the 

 body was Riidinger (1868), whose classic account of the comparative 

 anatomy of the muscles of the neck, shoulder, and fore-limb in Am- 

 phibia, Reptiles, Birds, and Mammals is quite well known. This 



