ON THE VERTEBRATE SKELETON. 283 
.) The Teeth. 
_. The bones of the dermo-skeleton are,— 
The Supratemporals ; 
_. The Supraorbitals ; 
. The Suborbitals ; 
The Labials. 
Such appears to be the natural classification of the parts which constitute 
the complex skull of osseous fishes. 
As the object of the present report relates chiefly to the endoskeleton, I 
have only added the osseous parts of the sense-capsules to the cranial vertebrae 
in fig. 5; omitting the branchial arches and dermal bones: the hemal arches 
and their appendages are given in diagrammatic outline. 
Reptiles—In proceeding with the inquiry into the natural arrangement of 
the skull-bones, I have selected from the Zeepétilia the crocodile, as a typical 
example of that class, and one most likely to facilitate the inquiry on account 
of the characteristic persistence of the primitive cranial sutures. 
Pursuing the same mode of investigation as in the case of the fish, let us 
disarticulate the hindmost segment of . 
the skull and so detach the four bones, Fig. 18. 
represented in fig. 18. The dotted ; 
circle indicates the points at which 
these bones are joined together, in 
order to encompass the epencephalon, 
or hindmost segment of the brain. 
No.1 is the centrum ; 2, 2 are the neur- 
apophyses with the coalesced par- 
apophyses (4, 4); and 3 is the neural 
spine. This element differs but little 
in size and shape from the similarly 
detached and depressed neural spine 
of the atlas of the crocodile. The Bn: ; ; 
single convex condyle at the back part _Disstticulated epencephalic such, viewed from 
of no. 1 makes that centrum resemble 
the posteriorly convex bodies of the 
trunk-vertebre in as striking a manner as the repetition of the articular 
concavity in the basioccipital of the cod (fig. 1,1) marks its serial homo- 
logy with the succeeding vertebral centrums of the same animal. In the 
descending process from the under part of the occipital centrum of the 
crocodile (fig. 18, 1), we see a second character of the cervical centrums in 
that reptile repeated, viz. their inferior exogenous spine. The neurapo- 
physes (2,2), like those of the atlas, meet above the neural canal: they give 
exit to the vagal and hypoglossal nerves, and protect the sides of the me- 
5 dulla oblongata and cerebellum, The neural spine (3) protects the upper 
Rn surface of the cerebellum: it is also traversed by tympanic cells, and assists, 
with the bones 2, 2, in the formation of the chamber for the internal ear. 
The special homology of the outstanding processes (4,4) in the crocodile 
and serpent (fig. 10), with the similarly situated but distinct ‘ paroccipital’ 
bones in the cod, is confirmed by their resuming their independency in the 
hinder segment of the skull of the chelonian reptiles; and the occipital neural 
_arch of the crocodile is reduced by their confluence with the neurapophyses 
to the condition of those of the trunk-vertebre, as composed, viz. of four 
instead of six elements. < 
The epencephalic arch offers the same simple condition not only in the 
ophidians but in most saurians: the chameleons however retain, like the 
u2 
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