Encyclopaedia Britannica > Volume 3, Anatomy-Astronomy

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Conijiara- man. While tlie quillet! duckbill (echidna, ornithorhyncus
Ibve hystrix) has only 15 ribs, the common duckbill (ornithor-
Anatomy. ]tyUCUS paradoxus) has 17; the horse and quagga have
18, the rhinoceros 19, the elephant and tapir 20, and in
the U7iau or two-toed sloth they amount to 23, which is
the greatest known number. On the whole, the most
prevalent number is 13. In the carnivorous animals they
are narrow and dense in structure. In the herbivorous
they are large, broad, and thick. In the armadillo the
two first ribs are large compared with the others. In the
two-toed ant-eater, which has 16 pairs, the}' are so broad
that they are imbricated over each other like the plates of
a corslet, and render the parietes of this animal’s chest
exceedingly solid. In the two species of duckbill (orni¬
thorhyncus paradoxus and hystrix ; echidna of Cuvier), the
true ribs, in number 6, consist of two portions—a long or
vertebral joined to the spine, and a short or sternal at¬
tached to the sternum. These portions are united by
cartilage, so as to resemble the ribs of birds. The 9 or
10 false ribs terminate before in broad, flat, oval plates of
bone, which are mutually connected by elastic ligaments.
The sternum, which is broad in the ourang and pongo,
is narrow in the other species of ape, and consists of seven
or eight pieces. In the vampyre and all the bat family
it is narrow, but presents before or below rather a promi¬
nent azygous ridge or keel (carina), and an anterior ex¬
tremity, broad on the sides, like a T, for receiving the
clavicles. In the mole the clavicular extremity of the
sternum is continued before the ribs, and is flat on the
sides for receiving the two short clavicles. In the hog
the sternum is broad behind and narrow before. In the
rhinoceros, horse, and elephant, it is prolonged before and
flat on the sides. In the Cetacea it is broad and thin,
especially before.
Cranium. Though the Quadrumana have 8 cranial bones, the
sphenoid often consists of two portions, one forming the
orbitar wings and the anterior clinoid processes, the other
the temporal or large wings, the posterior clinoid processes,
and the basilar fossa. The two parietal bones are early
united into one in the Chiroptera and the other Zoo-
phaga, in which, however, the frontal remains biparted
by a middle suture. The temporal tympanum is separat¬
ed from the rest of the bone by a suture, which is seldom
obliterated in the feline, canine, and viverra genera. The
temporal tympanum is also separate in the Rodentia, and
the frontal ununited. The parietal is united in some, as the
hare, the porcupine, cahia, marmot, rat, and squirrel; se¬
parate in the mouse, fat dormouse, and rabbit. The frontal
and parietal bones of the elephant are early united with
the other cranial bones, and form a vault without trace of
suture. In the hog, tapir, and hippopotamus, the two
parietal bones form one piece, while the frontal bone is
biparted ; and though in the rhinoceros both are biparted,
the frontal is early united into one portion. The sphe¬
noid bone of the animals of this tribe long consists of two
pieces, one forming the orbitar wing; the other the tem¬
poral wings, which, it is to be further observed, are the
smallest, in opposition to their proportional dimensions
in man. In the Ruminants and Solidungula the frontal
remains long parted by its middle suture; but the two
parietals are represented by a single bony vault. The
tympanum is always distinct from the temporal bone.
In the seal and walrus the parietal and the frontal con¬
sist of two pieces. The lamantin has only one bony arch,
representing the two parietal and the squamous part of
the temporal bones, while the temporal tympanum is de¬
tached from the rest of the bone. In the other Cetacea
the parietal bones are at an early period united to the oc¬
cipital and temporal bones, so that the five form one solid
poition. The auditory or pyramidal bone is always de-
" O M Y. 77
tached from the temporal, and adheres to the cranium bv Compara-
soft parts only. The sphenoid is not only long separate, tive
but consists of several portions. Anatomy.
1 hough, among the Quadrumana, the cranium of the
ourang-outang approaches that of man in shape, it differs
nevei theless in the connections of the constituent bones.
J he temporal wing of the sphenoid bone is very narrow,
does not reach the parietal, and touches the frontal only
by its upper extremity, so that the temporal bone is part¬
ly articulated with the frontal. The temporal suture is
not imbricated, but serrated. The same mode of connec¬
tion is observed in the mandrill, macaca (s. cynocephalus),
magot, and guenon (Cercopithecus), or tailed monkey
tribe. In the American monkey the temporal win<* of
the sphenoid touches neither the frontal nor the panetal
bones ; but the temporal bone is articulated directly with
the malar by its flat portion. In the American monkeys
the frontal bone does not touch the temporal wing of the
sphenoid, and the parietal is articulated to the malar. In
the howling ape (simia heelzebul) the connections are as
in man.
The connections of the cranial bones are in the Zoo- Connee-
phaga the same as in man. In the Rodentia the sphenoid t‘olls-
is joined to the frontal and temporal, without touching the
parietal; and the orbitar and temporal fossce are very small.
In the armadillo, pangolin, and sloth, the connections are
as in the Rodentia ; but in the ant-eater the parietal
bone, continued below the cranium, is united to the sphe¬
noid at the posterior part of the orbito-temporal fossa:.
In the elephant, though the cranial bones are at an
early period consolidated into one, the auditory is always
distinct from the temporal bone. In the hog, tapir, rhi¬
noceros, and hippopotamus, the sphenoid is united to the -
parietal bone, and its temporal wings occupy a small
space only of the orbitar and temporal fossae. The orbi¬
tar wings, though larger, appear small externally. The
auditory bone, though distinct, is, however, united by its
base to the margin of the auditory canal of the temporal
bone. The sphenoid of the ruminants is articulated, as
in man, with all the cranial bones; but its orbitar wing,
which is extensive, is principally concealed within the
cerebral cavity, and covered by the orbital part of the
frontal bone. In the Cetacea generally, all the sutures
which remain after early life are squamous or imbricated.
The outline of the frontal bone in the ourang-outang is
more irregular than in man, and the orbitar arches are
less surbased. In the American monkeys its outline is
triangular, and terminates in a point towards the vertex.
In the others of this family (Simia), this bone is almost
elliptical, and the orbitar arches are nearly straight; and
in the whole family these arches form, as in man, the an¬
terior border of the frontal bone, in consequence of the
narrowness of the root of the nose. In the makis it be¬
gins to widen, and the eyes become oblique,—a circum¬
stance which gives their frontal bone a rhomboidal shape.
The frontal bone in the Zoophaga, and in all the subse¬
quent Mammalia, except the Cetacea, forms an irre¬
gular prismatic or cylindrical surface with three faces—a
superior, bounded before by the muzzle, behjnd by the
cranial convexity and two lateral, descending into the or¬
bitar and temporal fossce on each side. The hedgehog,
mole, shrew, ant-eater, some of the phocce, the morse or
walrus, and the rhinoceros, have no proper orbitar arches;
and the frontal bone, though broad behind, is contracted
and nearly cylindrical between the orbits. In the hippo¬
potamus, the ruminants, and the onedmofed animals, it
enlarges, and forms a vault over each orbit. Lastly, in
the Cetacea it is narrow from before backward, resem¬
bling a fillet stretched across the cranium, but descends
beneath the maxillary bones to form the floor of the orbit.