XIX 



Duges to the cartilaginous glenoid region can be adopted, and the cora- 

 coid would then be represented (in part), rather by the element so named 

 by Owen. That eminent anatomist, however, reached his conclusion (only 

 in part the same as that here adopted) by an entirely different course of 

 reasoning, arid by a process, as it may be called, of elimination ; that is, 

 recognizing first the so-called &quot;radius&quot; and &quot;ulna,&quot; the &quot;humerus,&quot; the 

 * scapula,&quot; and the &quot; coracoid&quot; were successively identified from their rela 

 tions to the elements thus determined, and because they were numerically 

 similar to the homonymous parts in higher vertebrates. 



The detailed arguments for these conclusions, and references to the views 

 of other authors, will be given in a future memoir. I will only add&quot; here 

 that these homologies seem to be fully sustained by the relations of the 

 parts in the generalized Gauocephalous Batrachians (Apateon or Archego- 

 saurus, etc.). 



CHARACTERISTICS AND SEQUENCE OF PRIMARY 



GROUPS. 



Returning now to the consideration of tne primary classification of 

 Fishes, the results are submitted, in brief, of inquiries thus far instituted 

 into the limits, characters, and relations of the orders and including groups. 



While among the Mammals, there is almost 1 universal concurrence as to 

 the forms entitled to the first as well as the last places, naturalists differ 

 much concerning the &quot;highest&quot; of the ichthyoid vertebrates, but are all of 

 one accord respecting the form, to be designated as the &quot;lowest.&quot; With 

 that admitted lowest form as a starting-point, inquiry may be made re 

 specting the forms which are successively most nearly related. 



LEPTOCARDIA.NS. 



No dissent has ever been expressed from the proposition that the Lepto- 

 cardians (Branchiostoma) are the lowest of the Vertebrates ; while they 

 have doubtless deviated much from the representatives of the immediate 

 line of descent of the higher vertebrates, and arc probably specialized con 

 siderably, in some respects, in comparison with those vertebrates from 

 which they (in common with the higher forms) have descended, they un 

 doubtedly have diverged far less, and furnish a better hint as to the proto- 

 vertebrates than any other form. 



MARSIPOBRANCHIATES. 



Equally undisputed is it that most nearly related to the Leptocardians 



1 One eminent authority appears to think that the Cetaceans are the lowest and 

 most differentiated f Mammals, and, as a matter of fact, no one, it is presumed, 

 would dispute the proposition that the differences are more obvious, but they are 

 ideological, and not morphological; therefore, and in view of the gradation between 

 them and normal quadrupeds furnished by extinct types, naturalists are almost 

 agreed in denying the characters in question a taxonomic value equal to that accorded 

 to the differences exhibited by the Monotremes. 



