iherium by the great number and capacious size o f the air-cells which are in
communication with i t : these extend over all the upper, lateral, and back parts
o f the cranial cavity, as far even as the upper boundary o f the foramen magnum :
they also occupy the anterior two-thirds o f the basis cranii. T h e external configuration
o f the skull would, therefore, afford a very inadequate or rather
deceptive notion o f the capacity o f the cerebral cavity, were not the existence
and magnitude o f these sinuses known. The interspace o f the outer and inner
tables o f the cranium are separated above the origins o f the olfactory ganglia
for the extent o f three in c h e s : above the middle o f the cerebrum they are an
inch and a h a lf a p a r t; at the sides o f the cranium the interposed air-cells are
from one to two inches across; at the back part o f the cranium about one inch.
The sinuses have generally a rounded form.
The foramen rotundum, (through which in figure 3 a probe is represented
as passing), and the foramen ovale are situated close together, within a common
transversely oblong depression (i). T he carotid canal {g ) opens into the outer
side o f the commencement o f this wide channel, which conducts the great fifth
pair o f nerves to the outlets o f its two ch ie f divisions.
The petrous bone projects into the cranial cavity, in the form o f an angular
process with three fa c e t s : the foramen auditorium internum (A), and the aque-
ductus vestibuli, are situated on the posterior facet. Immediately behind the os
petrosum is the foramen lacerum jugulare (J), situated at the point o f convergence
o f the vertical groove o f the lateral sinus, with a groove o f similar s iz e continued
forwards from above the anterior condyloid canal. The plane o f the internal
opening o f this canal (c, fig. 3) is directed obliquely inwards and backwards, and
the lateral wall o f the foramen magnum behind the foramen condyloideum slopes
outwards to the edge o f the condyle. Immediately internal to the foramen condyloideum
is a small vascular foramen conducting a branch o f the basilar artery
into the condyloid canal, for the nourishment, doubtless, o f the great lingual
nerve.
In the relations o f the plane o f the internal orifice o f the anterior condyloid
foramen with that of the foramen magnum, we search in vain for a corresjjonding
structure in any o f the Mammiferous orders, save the E d en ta ta :* and among
these the Orycterope comes nearest the Glossothere in this respect. In the
degree o f development o f the internal osseous ridge giving attachment to the
tentorium cerebelli, the Ant-eaters and Armadillos more resemble the Glossothere
than does the O r y cterop e; in which a continuous bony plate arches across the
cranial c a v ity : in the Manis a still greater proportion o f the tentorium is ossified,
• In the monotrematous Echidna, the large canal for the lingiial i
course from tliat in the placental Edentata.
B lias a widely different direction and
and it consequently recedes the furthest amongst the Edentata, in this, as in most
other particulars o f the cranial organization, from the Glossothere. The chie f
distinctive peculiarity in the cranium o f the Glossothere, so far as it can be studied
in the present fragment, and compared with that o f other Edentata, is the deep,
well-marked, semicircular styloid depression, above described.
A question may arise after perusing the preceding evidence, upon which the
present fossil is referred to a great Edentate spe cie s nearly allied to the Orycteropus,
whether one or other o f the lower jaws, subsequently to be described, and
in like manner referable, from their dentition, either to the Orycteropodoid or D a sy -
podoid families o f Edentata, may not have belonged to the same spe cie s as does
the present mutilated cranium. I can only answer, that those jaws were d iscovered
by Mr. Darwin in a different and very remote locality,—that no fragments
or teeth referable to them were found associated with the present fo s s il; and that,
as it would be, therefore, impossible to determine from the evidence we have now
before us, which o f the two lower jaw s should be associated with Glossotherium;
and as both may with equal if not greater probability belong to a totally distinct
genus, it appears to me to be preferable, both in regard to the advancement of
our knowledge o f these most interesting Edentata of an ancient world, as well
as for the convenience o f their description, to assign to them, for the present, distinct
generic appellations.
The figures in P la te X V I . preclude the nece ssity o f a table o f admeasurements
o f the cranial fragment o f Glossotherium.
DESCRIPTION OF A MUTILATED LOWER JAW AND TEETH, ON W H IC H IS FOUNDED
A SUBGENUS OF MEGAT IIERIOID EDENTATA, UND ER TH E NAME OF
M Y L O D O N .
T h e genus Megalonyx, as is well known, owes its name and the discovery o f the
fossil remains on which it was founded, to the celebrated Jefferson,* formerly Pr esident
o f the United S tates. Cuvier, from an examination o f a single tooth, and
the ca sts o f certain bones o f the extremities, esp ecia lly the terminal ones, determined
the ordinal affinities o f this remarkable ex tinc t quadruped.f B u t while he
* Transactions of the Philosophical Society of Phlladclpliia, vol. iv. p. 246.
t Its relations to the Edentata, previously conjecfcui'cd by Dr. Wistar, are proved in the Annales du Sluseum,
tom. V. p. 358 ; its more immediate affinities as an aimcctant form in that group are discussed in the edition of
the Ossem. Fossiles, of 1833, tom. v. pt. 1. p. 160.