128 
FOSSIL REPTILIA OF THE 
B . Conclusion. 
Although a study of the evidences of Ichthyopterygian organisation, of which, and its 
modifications, as exemplified at the Liassic period, the results are given in the foregoing 
pages, has left the impression, mainly, of the great additions which wait to reward subse- 
quent cultivators of this field of comparative osteology, I am unwilling to quit it without 
giving expression to some of the general notions which its cultivation has suggested. 
Palaeontology has been regarded, if not defined, as including a kind of knowledge of 
parts, or of structures, in such degree interdependent that, any one being given, others 
may be deduced as a necessary consequence, such deductions being determinative of the 
relations of the whole ; so far as to give the Knower a power of predicating results, both 
zoologically, as respects the affinity of the otherwise unknown whole, of which only a 
part affects the senses, and physiologically, as respects the living powers of the whole and 
the part such extinct organism played in the sphere of its existence. 
This necessary connection and interdependency of the links of structures consti- 
tute the essential condition and attractive character of palseontological science. The 
subject, nevertheless, of the present Monograph, constrains me to submit the question, 
how far this science of ours has advanced towards sustaining the foregoing definition ; in 
other words, to how much of organic Nature at large, or of particular organisms, it is so 
applicable. 
Let us suppose, for example, that no other part of the petrified frame of an Ichthyo- 
saur had come to our hands than had reached those of Scheuchzer or of Bronn, — a few 
vertebral centrums, for example, from the hind part of the trunk. Could we have otherwise 
concluded than they did ? Certainly not, had our knowledge of the vertebral structures 
been restricted to the same parts of the extinct and fossilised animal. 
Biconcavity of centrums is a pre-eminently piscine character, but not without excep- 
tions in the class of Fishes, even in that great proportion of the species whose osseous 
development has advanced to individualised bony segments of the spinal column. Such 
an exception, e. g. we have in the opisthocoelian vertebrae of the Bony Gar {Lepidosteus). 
But no known kind of Fish possesses vertebral centrums with both upper and lower 
transverse processes (‘diapophyses’ and ‘ parapophyses ’). The presence of these in 
certain of the biconcave vertebrae of Icthgosaurus, bespeaks that of ribs having a two-fold 
articulation with their vertebrae ; and such structure of rib implies a body-cage adapted 
to the movements of expansion and contraction of its cavity, which cavity we infer, there- 
fore, to have contained bags receiving air, and to have had associated movements for the 
purposes of respiration. 
But this function raises the exerciser above the grade of the Fish, and the next ques- 
