56 PROFESSOR HUXLEY ON THE OSTEOLOGY OE THE GENUS GLYPTODON. 
aspect of the facet is backwards and downwards, so that, when viewed laterally, its 
plane appears inclined more than 45° to a horizontal line. The long axis of the facet 
is nearly at right angles to the axis of the skull, but its outer half has a slight inclination 
forwards and outwards. It will be observed that the direction of this facet corresponds 
very well with that of the articular facet on the condyle of the lower jaw of the new 
specimen ; and the nature of the articulation is such that the lower jaw must have had 
a purely hinge-like movement in a vertical plane, the doubly curved upper surface 
of each row of mandibular teeth being brought, with a simply crushing motion, 
against the correspondingly curved lower surface of the maxillary teeth in each masti- 
catory act. 
The “ deep and long groove ” into which, in the above description, the foramen rotun- 
dum is said to enter, requires particular notice. The foramen rotundum and the spheno- 
orbital fissure are represented by a rounded aperture 05 inch wide, situated immediately 
in front and to the inner side of the foramen ovale , and separated from it by only a 
narrow bar of bone. The small optic foramen, in like manner, lies immediately in front 
and to the inner side of this aperture, separated from it only by the lower root of the 
orbitosphenoid. 
The alisphenoid is prolonged forwards as a broad plate, parallel with the orbitosphe- 
noid, for about an inch ; and thus the conj oined foramen rotundum and Jissura spheno - 
orbitalis are continued outwards and forwards by a wide canal of the same length. Ante- 
riorly, the alisphenoid ends in an arcuated free edge, and so forms the hinder part of 
the outer lip of a groove open inferiorly, the inner wall of which is constituted by the 
lateral mass of the ethmoid. The front part of the outer lip of the groove, separated 
from the other by a slight interval, is formed by a strong descending vertical plate of 
the frontal bone, ending below in a rugose edge, thicker behind than in front, which 
sweeps upwards and forwards towards the posterior part of the infraorbital prominence. 
It ceases at about three-quarters of an inch from that part. 
The optic foramina are prolonged into canals directed forwards and outwards, each 
about an inch long, the anterior apertures of which open on the inner wall of the great 
passage just described, immediately behind the level of the anterior edges of the alisphe- 
noids. 
The optic nerves, which could hardly have been more than OT inch in diameter, and 
were therefore very slender in relation to the size of the animal, must have been con- 
tinued forwards between the frontal plate and the ethmoid for a distance of at least 
3^ inches before they reached the eyeball. 
Three other apertures are visible in the roof of the groove — one, about as large as the 
optic foramen, on its outer side, and three-quarters of an inch in front of the proper ante- 
rior end of the optic canal. The two others are smaller and situated close together, and 
rather on the inner side, half an inch in front of the former. These may be the ends of 
canals for the oculomotor nerves. 
The» remains of the expanded upper edge of a lamina perpendicularis, similar to that 
