542 Reviews. [July, 
nally distinct segments may be traced, This concordance in the 
arrangement of the cranial bones, composing these segments, he con- 
siders, “places the doctrine of the unity of organization of the ver- 
tebrate skull upon a perfectly sure and stable footing; ” whilst from 
the considerations already advanced, as to the non-segmentation of 
the cartilaginous bar in the- basis cranii, “the hypothesis that the 
skull is in any sense a modification of vertebree is clearly negatived.” 
The three segments, which Mr. Huxley traces throughout the series, 
are the occipital, composed of the basi-, ex-, and supra-occipital 
bones; the parietal, of the basi- and ali-sphenoids and parietal bones ; 
the frontal, of the pre- and orbito-sphenoid and frontal bones. These 
segments closely correspond with the central and neural portions of 
the occipital, parietal, and frontal vertebree of Oken, Owen, and some 
other morphological anatomists. But we would ask, is it not possible 
to trace a still greater number of segments—whether we call them 
vertebrae or not, is of little consequence to this part of our argument 
—in the cranium? Mr. Huxley does not, in the above generaliza- 
tion, limit his segments to the region in which, or to the parts of the 
' skull in relation to which, on his own showing, the notochord is 
confined. But, by accepting a presphenoidal segment, he admits of 
a cranial segmentation anterior to the pituitary fossa, i.e. in front of 
the spot where the notochord, as he contends, terminates anteriorly. 
Now, if the proposition be granted that the principle of cranial seg- 
mentation is not necessarily limited to the region of the notochord, 
but is applicable to the primordial cartilaginous cranium generally, 
we see no reason why, in those cases in which the structure and 
development of the skull admit of it, a still greater number of seg- 
ments should not exist, ethmoid, vomerine, or even rhinal, as the 
case may be. We may illustrate this by a reference to the mammalian 
head. In the head of the mammal alone the nasal cavities are fully 
completed. And there enters, in a most important manner, into their 
formation, a series of cartilages, the nasal cartilages, which remain 
unossified. One of these, forming a part of the nasal septum, is the 
anterior prolongation of the basal portion of the primordial cranium, 
and ought therefore to be taken into consideration in coming to any 
conclusion as to the number and nature of the cranial segments. But 
the septal and lateral nasal cartilages, also, are quite passed over by 
Mr. Huxley, in his determination of the segments of the skull. Now 
this we cannot but think is a most important omission, and one, too, 
which, if supplied, might still more strongly serve to show, than has 
been done in these lectures, that, though there is in some respects a 
unity of plan in the cranial structure of the pike and the man, yet that 
there is in others “a no less marked diversity, each type exhibiting 
structures and combinations peculiar to itself.” If the reception of a 
rhinal and a vomerine segment be objected to on the ground that they 
bear no relation to the neural axis, and differ in this, as in some other 
particulars, from the frontal, parictal, and occipital segments, it may 
be answered that at the caudal end of the spinal column great modifi- 
cations in the form and composition of the vertebral segments often 
occur ; modifications so great that the segment is often reduced to a 
