138 ANATOMY OF VERTEBRATES. 



serial homology of those piers, called \ neurapophyses,' viz., the 

 lamina? of the atlas, the exoccipitals, the alisphenoids, and the 

 orbitosphenoids, is equally unmistakable. Nor can we shut out of 

 view the same serial relationship of the paroccipitals, fig. 95, 4, as 

 coalesced diapophyses of the occipital vertebra, with the mastoids, ib. 

 8, and the postfrontals, 12, as par- or di-apophyses of their respective 

 vertebra?. All stand out from the sides of the cranium, as tranverse 

 processes for muscular attachment ; all are alike autogenous in the 

 Turtles ; and all of them, in Fishes, offer articular surfaces for the 

 ribs of their respective vertebra? ; and these characters are retained 

 in the postfrontals as well as in the mastoids of the Crocodiles. 



The frontal diapophysis, figs. 93, 95, 12, is wedged between the 

 back part of the spine, 11, and the neurapophysis, io; its out- 

 wardly projecting process extends backward, and joins that of 

 the succeeding diapophysis, 8 ; but, notwithstanding the retro- 

 gradation of the inferior arch, it still articulates with part of its 

 own pleurapophysial element, 28, which forms the proximal element 

 of that arch. 



There finally remain in the cranium of the Crocodile, after the 

 successive detachment of the foregoing arches, the bones termi- 

 nating the fore part of the skull, N 4, fig. 93 ; but, notwithstand- 

 ing the extreme decree of modification to which their extreme 

 position subjects them, we can still trace in their arrangement 

 a correspondence with the vertebrate type. 



A long and slender symmetrical grooved bone, fig. 93, 13, is con- 

 tinued forward from the coalesced pterygoids, 24, and stands in the 

 relation of a centrum to the vertical plates of bone, 14, which expand 

 as they rise into a broad, thick, triangular plate, with an exposed 

 horizontal superior surface. These bones, the prefrontals 14, stand 

 in the relation of neurapophyses to the rhinencephalic prolonga- 

 tions of the brain commonly called ' olfactory nerves ; ' and they 

 form the piers or haunches of a neural arch, which is completed 

 above by a pair of symmetrical bones, 15, called 'nasals,' which I 

 regard as a divided or bifid neural spine ; the independent basal 

 ossification, answering to the vomer in Fishes, figs. 81, 84, 13, and 

 Chelonians fig. 98 B, n, is in advance of its proper segment, and 

 divided in the middle line as in Ganoid Fishes and Batrachia. In 

 some Alligators {All. niger) the divided vomer extends far for- 

 ward, expands anteriorly, and appears upon the bony palate. 



Almost all the other bones of the head of the Crocodile are 

 adjusted so as to constitute four inverted arches. These are the 

 hsBmal arches of the four segments or vertebra?, of which the 

 neural arches have been just described. But they have been the 



