the known difference in the position o f the occipital plane, which in the Glossothere
corresponds with that in the Myrmecophaga and Bradypus, we shall be
justified in continuing to regard them, until evidence to the contrary be obtained,
as belonging to distinct genera.
The parietal bones present an oblong regular quadrate figure, the sagittal
suture running parallel with the squamous, and the frontal with the lambdoidal
suture ; there is scarcely any trace o f denticulations in the sagittal suture ; the
bones are o f remarkable thickness, varying, at this suture, from six to nine
line s, and their opposed surfaces are locked together b y narrow ridges, which
sligh tly radiate from the lower to the upper part o f the uniting surface : the
substance o f the bone consists o f an uniform and pretty dense diploe ; and there
are no sinuses developed in it. We can hardly regard the extraordinary air-cells
which occupy the interspace o f the two tables o f the skull in the parietal and
occipital bones o f the Glossothere (PI. X V I .. fig. 3) as a difference depending
merely on age.
The frontal and æthmoid bones are broken away in the present cranium. The
sphenoid commences two inches in front of the foramen occipitale; the fractured
sta te o f the skull does not allow its anterior or lateral limits to be accurately
defined; its body is occupied with large air-sinuses; the only part, indeed, o f this
bone which is exposed to observation is that which forms part of the floor o f the
cranium ; and this we shall now proceed to describe, in connexion with the other
peculiarities o f the cranial cavity, (fig. 1 . PI. X X I I I .) The body o f the sphenoid
is impressed on its cranial surface with a broad and shallow sella turcica («),
bounded by two grooves, {b b,) leading forwards and inwards from the carotid
foramina(c); the line o f suture between the sphenoid and occipital bones runs
along a slight transverse elevation(rf), which bounds the sella posteriorly; this
suture is partially obliterated: a sligh t median protuberance(e) bounds the sella
turcica anteriorly; there are neither anterior nor posterior clinoid processes.
External to the carotid channel there is a wide groove ( / ) leading to the foramen
ovale(_g); this foramen is about one-third smaller than in the Glossothere, and
therefore, as compared with the anterior condyloid foramina, indicates that the
tongue was endowed with a greater proportion o f sensitive than motive power in
the Scelidothere: but in reasoning on the s iz e o f this nerve, it must be remembered
that in both animals certain branches, both o f the second and third divisions of
the fifth pair o f nerves, are to be associated with the persistence o f large dental
pulps, o f which they regulate the secreting power. Anterior to the foramen ovale,
and at the termination o f the same large common groove, lodging the trunk o f the
fifth pair o f nerves is the foramen rotundum (A) ; this leads to a very long canal,
the diameter o f which is five lines, being somewhat le ss than that for the third
division o f the fifth pair. The anterior sphenoid is broken away, so that no
observation can be made on the optic foramina.
The basilar process o f the occipital bone is perforated at its middle by two
small foramina( 0 on the same transverse line, about h a lf an inch apart.
In the Armadillo these foramina do not e x i s t : in the Orycterope they are
present, but open beneath an overhanging ridge, which is continued from them to
the upper part o f the anterior condyloid foramen on each side. The sella turcica
o f the Orycterope is deeper and narrower than in the S celidothe re; and is separated
from the basilar occipital process by a transverse ridge, which sends forward two
short clinoid processes ; two smaller anterior clinoid processes project backwards
from the angle of the anterior boundary o f the sella turcica. T h e foramina ovalia
and rotunda open in the same continuous groove, as in the Glossothere and S c e lidothere,
but they are relatively wider a p a r t; and the canal for the third division
o f the fifth pair is shorter, and runs more directly outwards.
The petrous bone in the Scelidothere is relatively larger than in the Glossothere,
but this probably arises from the precocious development o f the organ o f hearing
in the present immature specimen in obedience to the general law. T h e trunk o f
the fifth pair o f nerves does not impress it with so deep and well defined a groove
as in the Glossothere; the elliptic internal auditory foramen(A) is situated about
the middle o f the posterior surface; behind this is the aqueductus vestib u li; and
immediately posterior to the petrous bone is the foramen ju gula r e (¿ ): the shape o f
the os petrosum agrees more with that o f the Armadillo than with that o f the
Orycterope. An accidental fracture o f the right os petrosum demonstrates its
usual dense and brittle texture, and at the same time has exposed the cochlea with
part o f its delicate and beautiful lamina spiralis. The conservation o f parts o f
the organs o f vision in certain fossils, has given rise to arguments which prove that
the laws o f light were the same at remote epochs o f the earth’s history as now i
and the structures I have ju st mentioned, in lik e manner, demonstrate that the
laws o f acoustics have not changed, and that the extinct giants o f a former race o f
quadrupeds were endowed with the same exquisite mechanism for appreciating
the vibrations o f sound as their ex isting congeners enjoy at the present day.
The brain, being regulated in its development by laws analogous to those which
govern the early perfection o f the organ o f hearing, appears to have been relatively
larger in the Scelidothere than in the Glossothere: it was certainly relatively
longer; the fractured cranium gives us six inches o f the antero-posterior diameter
o f the brain, but the analogy o f the Orycterope would lead to the inference that it
extended further into the part which is broken away. The greatest transverse
diameter o f the cranial cavity is four inches eight l in e s : these dimensions,
however, are sufficient to show that the brain was o f very small relative size in the
Scelidothere; and, both in this respect, and in the relative position o f its principal
masses, the brain o f the extinct E dental closely accords with the general characterof
this organ in the ex isting spe cie s o f the same Order. We perceive by the obtuse