THE OSTEOLOGY OF AMIURUS CATUS. 271 
the orbital muscles is exceedingly rudimentary, and very little 
cartilage remains in the skull, the anterior portion of the ethmoidal 
cartilage alone remaining unossified. 
1. SUPRAOCCIPITAL. 
This is the largest of all the occipital bones, but enters only very 
slightly into the boundary of the foramen magnum. Looking at it 
from above (Pl. II., Fig. 1, SO), it would appear to be divided into 
two portions, owing to the continuation backwards of the posterior 
fontanelle. Posteriorly, on either side of the fontanelle, it presents 
many minute foramina, belonging to the system of the mucous 
canals. Behind the posterior plane of the skull the bone is pro- 
longed into a long spine, from the under surface of which a triangular 
ridge (Pl. II., Fig. 2, SO) projects downwards and bifurcating above 
the foramen magnum is continued downwards on the exoccipital. 
On the posterior surface, on either side of this ridge, is seen a 
foramen, which, from the inner surface, opens into a canal formed 
by the union of two others. Of these the superior and larger is 
occupied by the ramus lateralis trigemini, the lower, separated from 
former by a small spicule, by the ascending branch of the first 
spinal nerve. Below this latter opening is a third, leading into a 
canal which traverses the substance of the bone, running downwards 
and outwards, and containing in the living state the canalis semi- 
circularis posterior. The supraoccipital articulates anteriorly with 
the frontals ; laterally with postfrontals, pterotics, epiotics and 
supraclavicle ; below with the epiotics, and ex-occipitals. 
2. Exoccrpirats (Pl. II1., Fig. 2, Ex0). 
Occupying the remainder of the boundary of the foramen magnum 
are the exoccipitals ; each of which forms the three sides of a cube 
open above, in front, and on the inner side. A ledge of bone pro- 
jects from the lower part of each bone inwards, meeting in the 
middle line, and forming the floor of the foramen magnum, and the 
root of the sinus impur. The ridge of bone extending downwards 
from the lower surface of the supraoccipital spine is continued down- 
wards on these bones, forming the lateral walls of the foramen 
magnum. On the outer surface are two foramina; the anterior 
small one gives passage to the nevus glossopharyngeus, and the pos- 
terior large one to the V. vagus. On the posterior surface is another 
