or THE VOMEE, ETHMOID, AHD INTEEMAXILLAEY BONES. 
309 
of the bird (sphenoido-frontals of Goodsie) must correspond with the frontals of the 
mammal ; and indeed they have the same relation to the cranial cavity, and are met, 
like those of the mammal, by the anterior extremity of a bone belonging to the series 
of centra. But if they are the frontals, then the bone which meets them, viz. the inter- 
orbital plate (prefrontal of Owex), corresponds to the mammalian central plate of the 
ethmoid, at least in the anterior part of its extent 
The Vomer in Bejptiles and Fishes . — Of the vomer in reptiles and fishes it is not neces- 
sary, for the purposes of this paper, to say much. If the vomer, palatals, and lateral 
masses of the ethmoid in the mammal form one segment, and if this segment is that to 
which the olfactory nerves belong, then it requires no argument to prove that these 
bones must be respectively represented in reptiles and fishes by the vomer and palatals 
of CuviEE and Owen, and the prefrontals ; for these comply with all the necessary con- 
ditions. The prefi’ontals and palatals are always in contact, and sometimes, as in the 
Crocodilia, in such a way as to indicate in the strongest manner that they are parts of 
one sclerotome ; while the vomer articulates always with one or other of these two pairs 
of bones, and sometimes with both. Moreover the vomer in reptiles and fishes always 
lies along the inferior margin of the septal cartilage (or middle frontal process of the 
primordial cranium). In reptiles, however, it presents a series of variations. While in 
the Turtle it is a single bone, and disposed much as in the mammal, except that infe- 
riorly it appears prominently in the palate f , in other reptilia it is in two parts — a right 
and a left. In the Crocodile these parts lie side by side, and interiorly articulate with 
the palate plates of the palatals, while superiorly they curve outwards and come in con- 
tact edge to edge with the superior extremities of the same bones. On the other hand, 
in the Serpents it is the inferior edges of the vomerine bones which curve outwards. In 
the Lizards they merely come in contact in the middle line ; and in the Batrachia they 
do not even meet. 
If it be asked, what corresponds in reptiles and fishes to the central plate of the 
ethmoid, I reply that it is the interorbital septum. This structure is frequently com- 
pletely ossified in fishes so as to form a single distinct bone ; and, as Professor Goodsie 
has pointed out J, it completes a neural ring with the great frontal. According to the 
theory now advanced, it differs from the central plate of the mammalian ethmoid only 
in that it stretches outwards and upwards to meet the frontal, instead of the frontal 
stretching downwards, spanning the whole arch to meet it ; and in that it does not pro- 
ject upwards in the middle line so as to divide the arch into lateral halves. 
According to this view the centrum of the frontal segment always lies between the 
* The posterior part of the interorhital plate appears to belong to the presphenoid, as has been pointed 
out by Professor Huxlet in his Lecture “ On the Theory of the Vertebrate Skull,” pp. 10 & 11. See Eoyal 
Society’s Proceedings, Nov. 18, 1858. 
t The vomer appears, however, in the palate of even some mammalia, viz. in certain Cetacea. In Hy- 
peroodon it even appears at two different places. 
+ Op. dt. p. 158. 
