Encyclopaedia Britannica > Volume 3, Anatomy-Astronomy

78 A N A T
Com para- The parietal bones of the ourang-outang differ from
tive those of man only in their temporal margin being nearly
Anatomy. straight. Those of the ape are narrower, and become more
oblique-angled as the cranium is flattened. In the Zoo-
phaga and Edentata they are almost rectangular. The
single parietal of the RodentiaIs nearly quadrilateral; but
it is sometimes flat, sometimes rounded, sometimes sur¬
mounted by a crest. Of the single parietal bone of the
ruminants, that of the stag, most of the antelope genus,
the sheep and the goat, is broad, and sends on each side
a narrow process into the temporal fossa before the occi¬
pital arch; in the camel it is narrower, and bears a lon¬
gitudinal crest; and in the ox and antilope bubalus it is
placed behind the occipital crest, and resembles a fillet
surrounding the back of the head transversely. In the
Solidungula the single parietal is nearly quadrilateral,
and placed before the occipital crest.
The occi- The occipital bone in the lower mammalia is remark-
pital bone, for fjVe characters. 1. The proper occipital surface,
instead of being oblique or horizontal, and inferior or ba¬
silar, becomes vertical and posterior. 2. The plane of
the occipital hole forms with that of the orbits an angle
constantly diminishing, becomes parallel to the orbitar
plane, and at length crosses it above the head. 3. The
plane of the occipital condyles, instead of being transverse
and horizontal, becomes oblique, and at length vertical.
4. The basilar or cuneiform process is not only hori¬
zontal, but forms with the occipital a right angle. And,
5. The mastoid process, which in man and the ape forms
part of the temporal, belongs in the other mammalia to
the occipital. In the polar bear, however, the mastoid
process constitutes part of the temporal bone.
From the 1st, 2d, and 3d characters, it results that the
head of quadrupeds is not balanced on the spine, but is
suspended by muscles, tendons, and ligaments, especially
the strong cervical, which connects the occipital spine to
the spinous processes of the cervical and dorsal vertebrae.
This ligament, therefore, though feeble and indistinct in
man, is strong, particularly in quadrupeds with heavy
head or long neck, in order to counteract the disadvantage
of the long lever. It is strongest in the elephant, and is
almost wholly ossified in the mole—a condition requisite
for the burrowing faculty exercised by that animal.
The tern- The temporal bone is naturally distinguished in the
poral bone. Mammalia into two parts ; a flat or proper temporal, cor¬
responding to the squamous part of the human temporal
bone, and the pyramidal, acoustic, or auditory, correspond¬
ing to the pyramidal or lithoid portion of the human sub¬
ject. The first only, which is proper to the scull, claims
attention here. In the ourang-outang and most of the
genus simia it forms a trapezium with the longest side
above, and the height of which varies with that of the
scull. In the American apes it is smallest in this direc¬
tion. In the Zoophaga the proper temporal bone is as in
the ape. Being narrow in the Rodentia behind, it is a
little rounded in the short-muzzled Edentata, the Rumi-
nantia, and Pachydermata.
The ethmoid is, strictly speaking, the olfactory bone,
and shall be mentioned under the organs of sense. The
sphenoid, among other offices, may be regarded as the
essential ophthalmic bone.
The facial The facial bones of the lower Mammalia differ from
bones. those of man ; first, in the number of separate pieces;
and, secondly, in the form and proportional horizontal ex¬
tent.
Intermax- The difference in number consists in each superior max¬
illary iuary being divided into a maxillary bone proper, and
bones* an anterior or labial portion; which being interposed be¬
tween the proper maxillary, are commonly denominated the
intermaxillary (ossa intermaxillaria). As it bears also the
O M Y.
superior incisors, it is named by Haller the incisive bone Compara.
(os incisivum); but since it is found not only in the rumi- tive
nants, which, excepting the camel, are void of incisors, but
in the Edentata and Cetacea, this denomination is less
applicable than the former. It ynuy be doubted whether
these should be regarded as additional bones, as they are
generally represented by zootomists ; for they are in truth
merely the incisive or anterior portion of the superior
maxillary bones. In other respects, the difference be¬
tween the human and the animal superior maxillary bone
is, that in the former each bone is in one piece, in the
latter it is in two. Even in the human foetus the trace
of the separation may be recognised ; and we have seen it
in the human scull some years after birth. Conversely,
it is early obliterated in some quadrupeds. Thus, though
distinct in the ourang-outang seen by Cuvier, it was not
found by Tyson or Daubenton, and is wanting in one pre¬
served in the Hunterian museum. In a young specimen
of the jocko also, noticed by Cuvier, no trace of the in¬
termaxillary suture was observed. It appears also to be
wanting in the perforated bat, the horse-shoe bat, and
the three-toed sloth.
Mutually united on the mesial plane, the intermaxillary
bones are united to the maxillary by sutures, which pass
from the outer angles of the latter, near the incisive holes,
towards the palate, where they intersect. In form and
size it varies in the different orders and genera. Small in
many of the Zoophaga and the walrus, it is large in the
Rodentia, in the hippopotamus, porpoise, and cachalot,
and prominent in the wombat. In the duckbill it consists
of two unciform portions, united by a broad intermediate
cartilage.
The peculiarity of the animal face consists in the ho- Elongation
rizontal elongation of the two jaw-bones. In the monkey of the face,
tribe this elongation is trifling; and all that is remarked
is, that the palate and maxillary bones are more elongated
in proportion to their height, and that their anterior part,
instead of being vertical, is more or less inclined forwards.
The degree of this elongation, which differs in different
genera, may be estimated by the acuteness of the facial
angle.
The narrowness of the interorbital space is another Interorbi-
character of the animal countenance. In the guenon and tal region.
American ape it is a mere septum ; but in the ourang-
outang, magot, and howler, it is larger, by reason of the
nasal fossce ascending to this height. From these the
face of the Zoophaga is distinguished by the following
circumstances. 1. The breadth of the ascending maxillary
processes throws the orbits to the sides; 2. these orbitar
surfaces form the anterior wall instead of the floor of the
orbit; 3. the malar bone is united neither to the frontal
nor to the sphenoid bone, and forms only the zygomatic
arch and the lower margin of the orbit; 4. the orbit, clos¬
ed neither behind nor below, communicates freely with
the temporal fossa ; and, 5. the palate bones are much
elongated and form a considerable spacg of the internal
wall, to which the ethmoid bone does not contribute. In
the Rodentia the interorbital space is still larger, by rea¬
son of the size of the intermaxillary bones throwing the
maxillary backwards and to the sides, where they form the
inner orbitar wall, in which the palate bones occupy only a
small space. The anterior wall is formed by a process of
the maxillary, which contributes to form the zygomatic
arch, while the malar is suspended in the middle between
the process and that of the temporal bone. Very similar
is the face of the elephant, except that the height of the
alveoli from the tusks, thrusting the nose upwards, and
shortening its bones, alters entirely the expression of the
head of this animal.
In the sloth, in which the face is short in proportion to