ON THE VERTEBRATE SKELETON. 191 
petrosal (16), and the retention by a great proportion of this capsule of the 
acoustic labyrinth of its primitive cartilaginous state, it occupies a smaller 
interval between the alisphenoid (6) and exoccipital (2). It no longer pro- 
trudes as a large bony wedge (as in figs. 6 and 7, 16) into the cranial eavity, 
but permits the alisphenoid to come into connection with the exoccipital. 
The result of this further retrogradation of the alisphenoid, in regard to the 
relative position of the outlet of the third division of the fifth, is analogous 
to that which occurs in the sheep. We saw in that mammal, through the 
recession of the squamosal, the foramen ovale advanced from the posterior to 
the middle part of the alisphenoid; in the crocodile, through the further re- 
moval from the cranial cavity of the interposed petrosal, the foramen ovale is 
advanced to the anterior border of the alisphenoid ; which border, in fact, it 
notches, the nerve escaping by a common foramen or ‘trou du conjugaison’ 
between the alisphenoid and the orbitosphenoid, the hole, however, being 
- principally formed by the alisphenoid (fig. 9, tr). This position of the ‘ fora- 
men ovale’ loses all its value as an argument in favour of the petrosal cha- 
racter of no. 6, by analogy with the position of the foramen ovale in man 
or the ape, when we take into consideration the necessary consequences of 
the successive withdrawal of the squamosal and true petrosal from the inner 
surface of the cranium in descending to the reptiles. The orbitosphenoid 
(fig. 9, 10), notwithstanding its great relative size, retains all its essential cha- 
racters: it is perforated or notched for the exit of the optic nerves (op) and 
first division of the fifth pair (s); it rests upon the presphenoid (9) kelow, 
and likewise, through its backward development, partly upon the basisphe- 
noid, and it articulates with the frontal (11) above, and also through the 
same backward extension with the parietal (7); it constitutes the anterior 
border of the lateral bony parietes of the cranium, which are interrupted 
by the orbits, and separated by their interposition in saurians and fishes 
from the rhinencephalic part of the cranial cavity (at 14, fig. 9). The cha- 
racters, in fact, of the orbitosphenoid are so clearly manifested in the cro- 
codile, that Cuvier, having been led by the increased share, as compared 
with mammals, which the crocodile’s alisphenoid (fig. 9, 6) takes in the form- 
ation of the otocrane, to regard it as the petrosal, and yet perceiving the 
essential characters of the orbitosphenoid in the bone (2d. 10) anterior to it, 
was driven to the conclusion that that bone represented both orbitosphe- 
noid (‘aile orbitaire du sphénoide’) and alisphenoid (aile temporale du sphé- 
noide). The cold-blooded crocodile, however, is not exactly the animal in 
which we should expect to find so unusual an instance of obliteration of 
sutures, as that between the alisphenoid and orbitosphenoid*. The actual 
and most characieristic modification of the orbitosphenoid in the crocodile’s 
skull, is its retrogradation together with the alisphenoid, or rather the main- 
tenance of its normal connection therewith by increased antero-posterior 
development, whereby it comes into communication above with the parietal 
(7) and below with the basisphenoid (5); whilst the alisphenoid, in like 
manner, gains a connection with the supra-occipital (3) above and the basi- 
occipital (1) below; although it still retains its more normal relations with the 
parietal, and rests in great part on the basisphenoid (5), as the orbitosphe- 
noid rests in great part upon the pre-sphenoid (9.) The superior connec- 
* No one better appreciated the characteristic persistence of the sutures in the crocodile 
than Cuvier, when his attention was not diverted from it by a favourite hypothesis. “Le 
crocodile a cela d’avantageux 4 l’étude de son ostéologie, que ses sutures ne s’effacent point, 
du moins n’en a-t-il disparu aucune dans nos plus vieilles tétes,” is the remark with which 
he commences his article on the determination of the bones of the head of that reptile 
(Ossemens Fossiles, 4to. v. pt. ii. p. 69): but at p. 76, a suture is assumed to be effaced, 
which is present in most mammals and all cold-blooded vertebrates, where a wider space 
does not intervene between the alisphenoid and orbitosphenoid. 
