COMPARATIVE ANATOMV. 
4. An os inter- 
maxillare. 
5. Two occipital 
condyles. 
6 . Seven cervical 
vertebras. 
Except the tliree- 
toed sloth, and some 
cetacea. 
7. Moveable dor- 
sal vertebr®. 
8. A pelvis closed 
in front. 
Except the ant- 
eaters ; which have 
it open : and the 
cetacea, which haVe 
none. 
9. True clavicles 9. Clavicles con- 
in a few genera stantly ; and almost 
Pnly. as universally the 
forklike bone. 
The structure of the cranium presents a 
very remarkable singularity in the elephant. 
Its two tables are separated from each 
other to a considerable extent, by nume- 
rous bony processes ; between which are 
formed a vast number of cells, communi- 
cating with the throat by means of the 
eustachian tube, and filled with air instead 
of the bloody or medullary substance, which 
occupies the dipliie of animals. The use 
of this structure in increasing the surface 
for attachment of those large musclas, which 
belong to the lower jaw, proboscis and 
neck ; and in augmenting the mechanical 
power of these muscles, by removing their 
attachments to a greater distance from the 
centre of motion, has been very ingeniously 
explained by Camper. ((Euvres, tom. 2). 
These advantages are attained by the cellu- 
lar structure, which we have just described, 
without augmenting the weight of the head, 
and this precaution is particularly necessary 
in the present instance, as the head is on 
other accounts more heavy and massy in 
this than in any other animal. The air 
cells of birds, in general, and particularly 
those which pervade the cranium in the 
ostrich, eagle, and owl, present examples 
of a similar formation, attended with the 
same uses ; viz. those of increasing the bulk 
and strength of the bone, and diminishing 
its weight. 
A comparison of the human cranium, 
witli that of animals, will lead us to some 
ffltereslina conclusions. Daubenton fixed on 
the situation of the foramen magnuin occi- 
pitale, as a point of comparison. He draws 
two lines, which intersect each other in the 
profile of the skull : one passes from the 
posterior margin of the great foramen, 
(which, in almost all mammalia, is also the 
superior one,) through the lower edge of 
the orbit; the otiier takes the direction of 
the opening itself, beginning at its posterior 
edge, and touching the articular surface of 
the condyles. He determines, according 
to the angle formed by the junction of 
these two lines, the similarity or diversity 
of the form of crania. 
This angle, is, however, but an imperfect 
criterion; for its variations are included 
between 80*' and 90“ in almost all quad- 
nipeds, which differ very essentially in 
other points. And small variations occur 
in the individuals of one and the same 
genus. 
The variations in the situation of the oc- 
cipital foramen are Important, when viewed 
in connection with the ordinary position of 
the animal’s body. In man, wffo is de- 
signed to hold his body erect, this opening 
is nearly equi-distant from the anterior and 
posterior extremities of the skull. The 
head therefore is supported in a state of 
equilibrium on the vertebral column. The 
angle, formed by the two lines mentioned 
by Daubenton, is only of three degrees. 
Quadrupeds, which go on all-fours, have 
the occipital foramen and condyles situated 
farther back, in proportion as the face is 
elongated. That opening, instead of being 
nearly parallel to the horizon, forms a con- 
siderable angle with it ; which, measured, 
according to Daubenton, is of 90 degiees 
in the horse. The weight of the head in 
these animals, is not therefore sustained by 
the spine ; but by a ligament of immense 
strength, which is either entirely deficient, 
or so weak, sis to have its existence dis- 
puted in the human subject. This liga- 
mentum muchse, or cervical ligament, arises 
from the spines of the dorsal and cervical 
vertebrae, (which are remarkably long for 
that purpose) and is fixed to the middle 
and posterior part of the occipital bone. 
It is of great size and strength in all qua- 
drupeds, but most particularly in the ele- 
phant ; where the vast weigiit of the head, 
so much increased by the enormous size of 
the tusks, sufficiently accounts for its in- 
creased magnitude. It is bony in tht: 
mole, pfobably on account of tlie use 
which the animal makes of its head, in dis- 
engaging and throwing up the earth. 
4. No os inter- 
maxillare. 
5. A single occi 
pital condyle. 
6. More than se- 
ven cervical verte- 
brae. 
7. Motionless dor- 
sal vertebrae. 
8. A pelvis open 
anteriorly. 
Except the os- 
trich. 
