THE MUSCULATURE OF THE TRUNK. 259 



entirely wanting. In the Struthious and short-winged 

 sea birds, in which the dorsal vertebrae are unfettered by 

 anchylosis, these muscles are more fleshy and distinct, 

 most so in the Ai^teryx'' [Anat. of Verts., vol. ii. 

 pp. 84, 85). 



From the fact that none of the muscles in the back 

 of such a form as the Raven exactly correspond with 

 the dorsal muscles of the Mammalia, and certainly not 

 with the highly differentiated groups, or the several 

 layers, as we find them in man, it is more than prob- 

 able that in the present instance I shall be called uj)on 

 to curtail and simplify their nomenclature, and bestow 

 upon certain ones provisional names, which they may 

 wear until such times as our knowledge of the myology 

 of the Yertebrata in general is far more extensive than 

 it is at the present time. 



AVe may hope for some light upon the question of 

 such homologies only through exhaustive and comparative 

 studies of the entire muscular systems of the Struthious 

 forms of existing birds, and such other types as Echidna, 

 the Duckbill, certain Fish forms, with such living Reptiles 

 as are known to approach these in their structure. At 

 the best, the unravelling of these homologies is an ex- 

 ceedingly difficult task, and one that demands all our 

 patience, as well as our keenest insight into morphological 

 problems. Not a little has already been accomplished in 

 the direction I point out, but very little as compared 

 with the enormous amount of exhaustive comparative 

 work that still remains in such fields, for the hands 

 and minds of the generations to come. 



We find in most existing Chelonians that these mus- 

 cles of the dorsum have almost entirely disappeared ; 

 while among the Snakes they are highly developed both 

 as regards complexity and differentiation. In living 



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