456 
from acting with sufficient mechanical advan- 
tage to extend the thigh as perfectly as in 
man. Vicq D’Azyr®* states, that in the Man- 
drills the flexors of the leg are inserted lower 
than the extensor muscles, and that they 
oppose the perfect extension of the leg upon 
the thigh, which renders it impossible for them 
to stand upright for any length of time without 
tottering. ‘The Chimpanzee, the Ourang-Outang, 
and some of the Gibbons, however, are ca- 
pable of walking upon their posterior extre- 
mities with the trunk nearly erect; but the 
poe being narrow, and the cotyloid cavities 
ing directed inwards so as to throw the soles 
of the feet very near each other, the base of 
support becomes very much contracted, and 
the animal stands very unsteadily. Of all the 
Quadrumana, the trunk of the Chimpanzee is 
directed nearest the vertical; in walking as 
well as in conformation he approaches nearest 
to the figure and gait of man. In the Hylo- 
bates and Laniscus the arms are of sufficient 
length to enable them to touch the plane of 
motion with the fingers and assist them in 
walking; this is resorted to whenever the 
centre of gravity falls anterior to the base of 
support formed by the hind extremities. 
I'he Lemurs are more decided!y quadrupeds ; 
the large are described by the spine, directed 
with its concavity downwards ; the lengthened 
horizontal direction of the face to the direc- 
tion of the scapular and cotyloid articulations, 
contribute to the prone position of the Lemurs. 
Some of the tribe, as the Lemur tardigradus, 
are denominated Sloths from their proverbially 
s'ow progression. Although the Ourangs have 
the advantage over other Quadrumana, of walk- 
ing erect, and having the hands and arms free 
for prehension and great variety of action, such 
as using a club for defence or assault ; yet the 
Gibbons outstrip the Ourangs in the velocity 
of their progression, and in their power of 
swinging and projecting themselves from tree 
to tree with extraordinary velocity. According 
to Duvaucel, the Hylobates agilis can launch 
itself from bough to bough at the distance of 
forty feet asunder, apparently without effort or 
fatigue. Martin relates, that “a live bird being 
set at liberty in the presence of a female Hylo- 
bates agilis, she marked its flight, made a 
long swing to a distant branch, caught the 
bird with one hand in her passage, and at- 
tained the branch with her other hand, her 
aim both at the bird and the branch being as 
successful as if one object only had gained 
her attention.” The addition of a long and 
flexible tail in the Cercopithecus, Semno- 
pithecus, and several other species, gives a fifth 
organ of prehension which is employed to as- 
sist them in a variety of motions. The walk, 
trot, and gallop of the Quadrumana are per- 
formed upon their four extremities on the same 
neiples as those of quadrupeds in general, 
ut as plantigrade bipeds their locomotion is 
accomplished like that of man. 
Secr. V. Man.—The locomotion of man 
is that of a plantigrade biped. When the 
* System Anat. des Animaux. 
MOTION. 
body is erect and the face inclined ata s! val 
angle above the horizontal plane, the head is 
exactly balanced on the atlas, and its weight is 
transferred to the latter with the least expen 
diture of muscular action: its axis of motion 
is bisected by a vertical line passing through its 
centre of gravity when it is in equilibrio upon 
the atlas: in every other position of the head 
the expenditure of muscularaction is increased. 
It has 5 a observed by Daubenton, that, vhe 
in the position of a quadruped, man is obliged 
to elevate the head above the axis of the ver- 
tebral column, in order to see directly for- 
wards; and in depressing the head to the 
earth, the position of the occipito-atlantal arti- 
culation prevents the jaws reaching the ground, 
The movements of the head on the atlas are — 
restricted to one plane, namely, the vertical 5 
but its articulation with the dentata permits 
a horizontal motion through a large are of a 
circle ; the head cannot turn without the atlas, 
nor the atlas without the head; on the con- 
trary, the atlas and dentata revolve upon each 
other in opposite directions. By means of 
these two joints, whose axes of motion are ¢ 
right angles to each other, the head enjoys a 
considerable range both in the vertica 
horizontal planes. a 
The vertebral column.—The office of this 
complex structure is purely mechanical. The 
flexibility of the spine 1s due to the twenty-foui 
joints which divide its length, and the interposi- 
tion of the elastic, intervertebral, fibrous tissues. 
It is upon the elasticity and quantity of the latte 
that the flexibility of the vertebral column de 
pends. The mean proportions of the heights of 
the cervical, dorsal, and lumbar intervertebral 
elastic tissues to that of the bodies of the ver- 
tebre are estimated by Weber as follows: _ 4 
Heights of cervical vertebrae .... 
Dorsal sal 
Lumbar ,, 
Heights of intervertebral tissues. . 
Cervical 3 oe 
Dorsal > a 
Lumbar a: o 
and their mean diameters, 
28.0 “| 
And, admitting their breadth to be equal 
their thickness, which is near the truth, # 
tranverse sections will be as the — f 
breadths, or as 225, 640, 784. Hence, if 
cervical, dorsal, and lumbar portions are cury 
with equal force, their angles of flexion ¢ 
their elasticity will be in the following 
portions : 4 
(2) : @) an 
2257 © \6407 ~ \7B4 " | 
846 : 297 ; 298 lam | 
that is, the angle of flexion of the dorsal a 
lumbar portions, notwithstanding their 
lengths, are nearly equa!, whilst the angle 
the cervical portion, though of much | | 
; 
& 
‘i 
