130 DR. T. S. COBBOLD ON THE CRANIAL BONES [April 8, 
in respect of the individual elements of which it is composed. Three, 
or at most four, bones enclose the cranial cavity ; whilst four others 
form the face, two being concerned in the formation of the jaws. 
Besides these there are several osseous appendages, including the 
hyoid apparatus. 
Conynencing from behind forwards we find two lateral occipital 
bones (A, fig. 1), forming the posterior part of the cranial vault. 
From the side they exhibit a triangular outline ; but their bases con- 
verge internally so as to form part of the floor of the cerebral cavity. 
At the middle line below, they unite, leaving, however, a small central 
interspace, through which may be seen the posterior part of the 
sphenoid bone; on this latter the occipitals rest. Intimately con- 
nected with the posterior border of these occipitals are two vertebral 
laminze (B) supporting a single neural spine (C) ; and immediately 
behind these there are two other laminz (D), surmounted by a double 
neural spine (EH, E). All these elements rest upon the posterior 
part of the sphenoid bone, which may be looked upon as an ossified 
prolongation of the chorda dorsalis. ' 
Opposite the point of union between the lateral occipitals and the 
sphenoid we find two remarkable appendages (F, F). These rib- 
like elements project obliquely backwards on either side, and form 
cylindrical rods, having a tolerably uniform thickness throughout. 
Notwithstanding the objections which may be raised, I am inclined 
to regard these bones as cranial ribs. They are placed above and 
behind the clavicular arch ; and, as Bischoff remarks in Lepidosiren 
paradowa, it is clear from their articular connexions that they cannot 
be regarded as styloid processes. 
The sphenoid bone (G), seen from below (fig. 3), is spathulate. 
With the exception above mentioned, it forms the entire floor of the 
cranial cavity. It is concave at the anterior half, both above and 
beneath, and, consequently, also channeled out on either side. The 
posterior narrow end is convex inferiorly, where it likewise displays 
a T-shaped groove for the partial lodgement of the aorta. The 
sphenoid is relatively longer, and terminates more abruptly in front, 
than the corresponding bone in Lepidosiren paradoxa. 
The vault of the cranium is also for the most part covered in by a 
single bone (H). This I believe to consist simply of the two con- 
joined parietals; but Bischoff thinks the frontals are likewise in- 
cluded in the mass. The appearance of the bone very strongly mi- 
litates against this latter view, inasmuch as two ossific centres are 
clearly discernible at the anterior third on either side, and from these 
two points the osseous spiculze radiate in all directions.  Deserip- 
tively it may be regarded as consisting of three laminze united in the 
central line, the two lower forming the cranial roof, and the upper 
and somewhat thicker plate constituting a longitudinal vertical ridge, 
analogous to the parieto-occipital crest in Carnivora. “ 
If the above view be correct, I think it will be admitted that the 
singular pair of bones overlapping the parietals can be none other than 
the frontals (I, I, figs. 1, 2); but Bischoff conjecturally assumes 
them to be the cheek-bones. That the malar bones should be found 
