BY W. J. S. McKAY. 291 



in Cryptobranch its supeificial fibres are blended with the under- 

 surface of the pectoral, and that in Crocodile the fibres that 

 correspond with it form part of the origin of the pectoral. It 

 thus, to some extent, occupies the place of the ])ectoralis minor ; 

 and if we suppose it continued upon the under surface of the 

 pectoral, and in variable degrees segmented from that muscle, it 

 would quite correspond with the ordinary Mammalian i)ectoralis 

 minor, the proper insertion of which appears to be the radial ridge 

 or tubercle of the humerus. It is, however, in man, and some 

 animals, arrested wholly, or (Rat) partially, at the coracoid, and is 

 often quite segmented from the pectoralis major. Thus, I conceive 

 the pectoralis minor to be formed from factors of the pectoralis 

 major, which, or some of which, repi'csents the epicoraco-humeral 

 of Urodelans, Reptiles, and Monotremes, and that it also in part 

 represents, indeed is the nearest representative of, the levator 

 humeri of Birds." 



( M. COSTO-CORACOIDEUS. 

 M. SUBCLAVIUS<^ 



I M. STERNO-EPICORACOIDEUS. 



Echidna : M. costo-coracoidtus, M. sterno-coracoideus, We.stling : 

 Suhclavius, Mivart. 



Ornithorhynchus : Suhclavius [?), P. minor (?), Meckel, Owen, Coues. 



ECHIDKA. 



Origin, {a) M. costo-coracoideus. — This muscle arises from 

 the sternal three-quarters of the anterior border of the first rib. 

 (Fig. 4, A. Cc). 



Insertion. The muscle is fan-shaped in outline, and runs 

 forward, the fibres converging to a small tendon by which the 

 muscle is inserted on the dorsal surface of the coracoid bone 

 immediately adjoining the coraco-presternal arthrodia; while some 

 of the inner fibres are attached to the postero-external part of the 

 dorsal surface of the epicoracoid. 



Relations. The dorsal aspect of the muscle is hidden in 

 part by the sterno-coracoid, which lies internal to it ; while it is 

 placed dorsal to the origins of the coraco-brachialis longus et 



