Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25759/304/
292 
AV ES. 
and into the sides of the lower jaw from the 
articulation as far forward as the commence¬ 
ment of the horny bill. 
In the Cormorant there projects backwards 
from the spine or squamous element of the 
occipital bone, an osseous style about an inch 
in length, of a trihedral figure and tapering to 
a point. It is not anchylosed as a process of 
the occiput, but is moveably articulated to it ; 
and its description has been referred to this 
section because it does not constitute a regular 
part of the skeleton, not representing any 
essential element of the bony fabric, but is to 
be regarded like the bony tendons of the legs 
as an ossification of the intermuscular aponeu¬ 
rosis of the temporal muscles to which it 
affords a more extensive and firmer origin. 
This, indeed, is its essential use,* for the mus¬ 
cles of the upper part of the neck are inserted 
into the occipital bone, and glide beneath the 
posterior or superadded fasciculi of the tem¬ 
poral muscle. Analogous parts appended to 
the true spinous processes of the vertebrae are 
met with abundantly in the inferior vertebrate 
classes, especially in fishes, where they extend 
frequently above the spines of the whole ver¬ 
tebral column, increasing the surface of origin 
of the lateral series of muscles. 
The muscle analogous to the Biventer 
maxilla (18) arises by two portions, the one 
from the lateral depression of the occiput, the 
other from the depression behind and below 
the external meatus auditorius ; they are in¬ 
serted into the back part and angle of 
the lower jaw. A similar disposition of 
the digastricm is met with in many of the 
mammalia; even in the Orang-utan (Simla 
Satyrus) it is equally devoid of a central 
tendon, and is unconnected with the os hyoides. 
The openers and closers of the mandibles 
present very slight differences of bulk in rela¬ 
tion to the development of the parts they are 
destined to move; their disproportion to the 
bill is, on the contrary, truly remarkable in the 
Horn-bills, Toucans, and Pelican, and the bill 
is but weakly closed in these in comparison 
with the shorter-billed birds. - 
The upper mandible is moved by three 
muscles on either side. The first is of a radiated 
form, arises from the septum of the orbits, and 
converges to be inserted into the external and 
posterior end of the pterygoid bone, just where 
this is articulated to the tympanic bone. It 
draws forward the pterygoid bone, which pushes 
against and raises the upper jaw. 
The second muscle analogous to the External 
Pterygoid arises from the space between the 
posterior part of the orbit and external meatus 
auditorius, and is inserted into the internal 
process and contiguous surface of the tympanic 
bone; it affects the pterygoid process,and con¬ 
sequently the upper mandible in the same 
way as the preceding muscles, and assists in 
opening the bill. 
The Pterygoideus Internus is a long and 
* See Yarrell * On the Anatomy of the Cormo- 
ant/ Zool. Trans, v. iv. p. 235. 
slender muscle ; it arises from the pterygoid 
process and body of the sphenoid, and is in¬ 
serted principally into the inner side of the 
lower jaw and tympanic bone ; it also sends 
off a small tendon to the membrane of the 
palate. This muscle draws forward the lower 
jaw and depresses the upper one. 
In the Cross-bill (Loxia curvirostra) there 
is a remarkable want of symmetry in the 
muscles of the jaws on the two sides of the 
head corresponding to their peculiar position. 
Those of the side towards which the lower 
jaw is drawn in a stale of rest (which varies 
in different individuals) are most developed, 
and act upon the mandibles with a force that 
enables the bird to dislodge the seeds of the 
fir-cones, which constitute its food. 
The articulation of the lower jaw is strength¬ 
ened and its movements restrained by two 
strong ligaments, one of these (a) is extended 
from the ligament completing the lower part 
of the orbit, or from the zygomatic process of 
the temporal bone, and is inserted at the outer 
protuberance near the joint of the lower jaw, 
and must prevent the bill from being too 
widely opened. The second ligament extends 
from the zygomatic process of the temporal bone 
directly backwards to the posterior part of the 
articular depression of the lower jaw, and is 
designed to guard against the backward dislo¬ 
cation of the lower jaw. 
The muscles of the ribs. — The levatores 
costarum arise from the posterior part of the 
extremities of the transverse processes, and 
converge to be inserted into the anterior 
margin of the succeeding posterior rib. Those 
of the first and second ribs represent the 
Scaleni, and are of larger size, arising from 
the last and penultimate cervical vertebrae. 
The Intercostales extemi appear to be con¬ 
tinuations of the Levatores costarum, and are 
usually divided into an anterior and posterior 
moiety corresponding to the marked separation 
and moveable articulation between the vertebral 
and sternal portions of the ribs ; the anterior 
division arises from the costal appendage and 
extends to the anterior extremity of the rib ; 
to afford a more advantageous origin to this 
inspiratory muscle would appear, therefore, to 
be one of the uses of the costal appendages, 
as well as to strengthen the connection of the 
ribs to each other. 
The Internal intercostals commence at the 
sternal extremities of the ribs, as in mammalia, 
but extend backwards no farther than the costal 
appendages; their fibres run in an opposite 
direction to the external intercostals, and are 
shorter, the insertion into the posterior suc¬ 
ceeding rib being by a thin but wide aponeu¬ 
rosis : in the Penguin they are, however, 
wholly muscular. Two other layers of inter¬ 
costal muscles, corresponding to the triangu¬ 
laris sterni, and having the same direction 
of fibres, are extended from before backwards 
and outwards to the four anterior sternal por¬ 
tions of the ribs ; arising from the superior and 
external angle of the sternum. 
The muscles of the abdomen are small and
        

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