54 PROFESSOR HUXLEY ON THE OSTEOLOGY OE THE GENUS GLYPTODON. 
pterygoid processes in the direction towards the antorbital foramen. The base of the 
zygomatic process supporting the articulation of the lower jaw (m) is brought much 
nearer the occiput than in the Mylodon , and is separated from the petromastoid by a 
deep excavation, perforated by wide apertures that seem to communicate with the tym- 
panic cavity. The articular surface for the lower jaw is well defined, narrow in the axis 
of the skull, much extended transversely, gently convex in both directions. In the 
skull of a recent Armadillo ( Dasypus octocinctus ) the articulation for the lower jaw is 
almost flat, and on a level with the roof of the posterior perforated cavity. In the Prio- 
nodon {Dasypus gig as, Cuv.) the articular surface is slightly concave, and extends longi- 
tudinally forwards from the posterior cavity. The zygomatic process of the malar bone, 
bounds the outer and fore part of the surface, and extends forwards in the form of a 
laterally compressed plate of bone, and in the Das. sexcinctus forms a slight angular 
projection below the antorbital perforation. In the Glyptodon , the articulation for the 
lower jaw more resembles that in ordinary Pachyderms, and is thus conformable with 
the deviation from the Edentate structure manifested by the bones of the foot. But 
the most remarkable characteristic of the skull of the Glyptodon , by which it differs 
from the existing Armadillos and approaches the Megatherioids, is the long and strong 
process (n) which descends from the base or origin of the zygomatic process of the maxillary 
bone. This process is compressed, but in the opposite direction to that in the Mylo- 
don. , viz. from before backwards, instead of from side to side ; it measures five inches in 
length from the antorbital perforation, one inch and three-fourths in breadth across the 
middle : the outer margin is entire, and as if folded back ; the lower half of the inner 
margin is slightly notched, the extremity of the process curves backwards. Both ante- 
rior and posterior surfaces bear strong marks of the attachment of muscular fibres. 
“ The small remaining portion of the maxillary bone- on the inner side of this process 
shows portions of three deep sockets (o o ) of the same diameter throughout, indicating the 
implantation of molar teeth by a single excavated base, and showing two longitudinal 
ridges on both the outer and the inner side, which proves the teeth to have had the 
same fluted exterior which they present in the lower jaw, and of which the generic 
name of Glyptodon is expressive. The fractured anterior part of the basis cranii shows 
the large cavities for the olfactory bulbs, and the remains of a very extensive cribriform 
plate, the organ of smell being very largely developed. 
“ The posterior, or occipital surface of the skull slopes forward from the plane of the 
occipital foramen at an angle of 45° ; in the small existing Armadillos it is vertical ; in 
the Glyptodon it is divided by a strong median vertical ridge, and separated by a sinuous 
thicker transverse ridge from the upper surface of the skull. The posterior half of this 
region of the cranium is marked by the ridges bounding the origins of the temporal 
muscles, which almost meet along the middle or sagittal line. Part of the lambdoidal 
suture is seen at p ; the other cranial sutures are obliterated. The temporal fossae are 
pierced by numerous large vascular foramina. The anterior parts of the temporal 
ridges (g) diverge to the posterior angle of the supraorbital ridges. The frontal or inter- 
