CKANIAL VEKTEBR.E. 615 



(1646.) Any given appendage, however, as Professor Owen * justly 

 observes, might have been the seat of such developments as convert that 

 of the pelvic arch into a locomotive limb ; and the true insight into the 

 general homology of limbs enables us to point out many potential pairs 

 in the typical endoskeleton. The possible and conceivable modifications 

 of the vertebrate archetype are far from having been exhausted in the 

 forms that have hitherto been recognized, from the primaeval fishes of 

 the palaeozoic ocean of this planet up to the present time ; or, in other 

 words, it would be by no means contrary to the general laws of 

 osteogenic development, however different from the ordinary course of 

 nature, were vertebrate animals to occur possessed of more than the two 

 pairs of locomotive extremities usually conferred ; so that such beings 

 as hippogriffs and other winged quadrupeds, however fabulous, would be 

 by no means monstrous productions. 



(1647.) As the segments approach the tail in the air-breathing verte- 

 brates, they are usually progressively simplified, first by the diminution, 

 coalescence, and final loss of the pleurapophysis, next by the similar 

 diminution and final removal of the ha3mal and neural arches, and some- 

 times also by the coalescence of the remaining central elements, either 

 into a long osseous style, as in the Progs (fig. 333), or into a shorter 

 flattened disk, as in many Birds. In Fishes, however, the seat of the 

 terminal degradation of the vertebral column is first and chiefly in the 

 central elements, which in the Homocercals, i. e. in those genera which, 

 like the Perch (fig. 311), have a symmetrical bilobed tail, are commonly 

 blended together, and shortened by absorption, whilst both neural and 

 haemal arches remain with increased vertical extent, and indicate the 

 number of the metamorphosed or obliterated centrums. 



(1648.) The anterior vertebrae of the spinal series are modified in 

 their form and dimensions in proportion to the increased development of 

 the anterior part of the cerebro- spinal axis, and that to such an extent, 

 more especially in the mammiferous races, that their real nature and 

 character are completely masked from ordinary observation, neverthe- 

 less guided by the principles above laid down, that the bones of the 

 cranial portion of the spinal column conform in their essential arrange- 

 ment with what has been observed in the rest of the vertebral series, 

 and that the skull is in reality made up of the same elemental parts, 

 modified, it is true, to a very remarkable extent, yet still recognizable, in 

 accordance with just principles of philosophical induction, as the homo- 

 logues of those described above. 



(1649.) The cranial bones, when examined by any unprejudiced ob- 

 server, readily resolve themselves into four distinct vertebrae, which 

 may be named, reckoning them from behind forwards, the 



* " On the Archetype and Homologies of the Vertebrate Skeleton." London : 

 John Van Voorst. 



