10 



might once have been said that tlic jaws did not partake of the intermediacy, 

 because they all present teeth, and are never smooth, like those of birds. Yet 

 birds with teeth have recently been discovered, which deprives us of the use 

 of this character as a definition. In the discoglossid frog, the cranium is not 

 intermediate in structure between the frog and salamander, but is that of a 

 trog. Ill tiie Loxolophodon, the toothless front of the upper jaw is not a 

 general character of either of the orders between wliich it stands. 



These difficulties arise from the existence of the subordinate variations 

 or subtypes of a general or major pattern, and, for their resolution, require 

 only a new application of the first law of uniformity on the lower plane. If 

 the subcharacters defining the subpattern be known, the existence of one 

 presupi^oses that of the others. The structure of an artiodactyle astragalus 

 will not enable me to infer the character of the incisor-teeth of the animal; 

 for this I require some other more minutely-correlated portion. So I can 

 infer the ribs and vertebrae from the sternum of the discoglossid frog, but n(jt 

 the cranium ; for this I require some part correlated with discoglossid char- 

 acters only, and not only significant of the relations to the orders of Batra- 

 chians, as are the characters mentioned, although it happens, by the accident 

 of discovery, that none but such frogs are known to possess them to-day. 



The two laws vyliich further aid the deductions of the paleontologist are 

 those of mechanical relations and of embryonic parallelism. One structure 

 requires another in order that an animal be viable. Thus, long legs in a grazer 

 presuppose a long neck to enable it to reach the ground with its lips. Hooked 

 claws presuppose carnassial teeth or a hooked beak. For a horizontal body 

 to be properly poised on two legs instead of four, the weight of the viscera 

 must be transferred backward, and the anterior regions of the body lightened. 

 This we find to be the case with birds and Dinosauria. The lower bones of 

 the pelvis, with the contained organs, ai-e thrown backward, while the fore- 

 limbs are lightened and the head reduced in proportionate (not absolute) size. 



The parallelism of types with transient embryonic conditions of other 

 types, aids the paleontologist essentially in the classification or proper location 

 of a specimen. Its relation to known series must be first determined, as this 

 obviously precedes in reconstruction all application of tlie law of uniformity. 

 Such reference having been made, either to a new series or to a place in a 

 known series, the considerations heretofore adduced come into view, but not 

 sooner. Hence, the law of parallelism is as essential to the paleontologist, as 

 it is all-pervading and all-expressive of nature itself. 



