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 (PI. II., Fig. 1, SO), it would appear to be divided into 

 two portions, owing to the continuation backwards of the posterioi 

 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 (PI. 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- 

 circidaris posterior. The supraoccipital articulates anteriorly with 

 the frontals ; laterally with postfrontals, pterotics, epiotics and 

 supraclavicle ; below with the epiotics, and ex-occipitals. 



2. Exoccipitals (PI. II., Fig. 2, ExO). 



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 

 roof of the sinus impar. 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 fo^'amen 

 magnum. On the outer surface are two foramina ; the anterior 

 small one gives passage to the nervus glossopharyngeus, and the pos- 

 terior large one to the N. vagus. On the posterior surface is another 



