542 
tionate to the violence of the impulse required 
in rath the tail, and occupying the lateral 
regions of the body, extend quite from the head 
to the caudal fin, constituting almost the entire 
bulk of the animal, and possessing sufficient 
strength from their combined contractions to 
scull the fish through the water with surpris.ng 
velocity, or even to enable the salmon to throw 
itself up the cataract, that bars its progress up 
the river, where it is commissioned to lay its 
During the changes that accompany the de- 
velopement of the tadpole, which by its meta- 
morphosis into a frog is literally converted from 
the condition of a fish into that of a reptile, the 
transmutation observable in the pi Se of 
the muscles acting upon the spine are not less 
remarkable, than those witnessed in the verte- 
bral column itself. Whilst in its tadpole state 
the frog is, as regards its powers of locomotion, 
strictly a fish, and rows itself about entirely by 
the movements of its expanded vertical tail 
exactly as fishes do, but as the limbs of the 
reptile gradually make their appearance the 
lateral muscles of the spine that previously 
formed the bulk of the creature are absorbed 
and disappear, the hitherto flexible and elon- 
gated vertebral column becomes short and but 
little gifted with motion, and its muscles in 
the same ratio grow feeble and unimporta: t, 
In the other forms of Rept.les, as well as in 
Birds and Mammalia, the muscular system 
acting upon the vertebral chain presents great 
uniformity of character, the number and strength 
of the muscular fasciculi being exaggerated, or 
diminished in different regions in proportion as 
mobility is permitted, the movements of the 
spine being generally diminished, and tram- 
melled in exactly the same ratio as the loco- 
motive limbs become more perfect and efficient. 
2. The costal muscles form a system apart, 
quite independent of those connected with the 
vertebral column, and exactly keeping pace 
with the developement of the skeleton of the 
thorax. In Fishes a thoracic cavity cannot be 
said to exist, inasmuch as the ribs that enclose 
the viscera seem rather processes fixed to the 
spine, in order to give a greater extent of sur- 
face for the attachment of muscles destined to 
act upon the tail, than properly the representa- 
tives of the costal elements of the skeleton ; 
neither do ribs exist in the tadpole, or even in 
the perfect frog. Even in those Batrachia that 
are most gifted in this particular, minute corni- 
cula appended to the apices of the transverse 
processes of the vertebra are the only rudi- 
ments of a costal system of bones, and these 
muscles are vainly looked for. 
In the Tortoises and Turtles likewise, al- 
though both vertebral and sternal ribs are 
present, and so hugely developed that they con- 
stitute the great bulk of the earapax covering 
these strange reptiles, such is the immobility 
of the dorsal shield, and so securely are the 
ribs conjoined by suture, that any muscular 
apparatus destined to act upon them would 
have been obviously superfluous. 
In Serpents, however, the case is widely 
different ; for in these lithe and limbless crea- 
MUSCULAR SYSTEM. 
tures the ribs are made to serve as most impor-_ 
tant locomotive agents, and their movements — 
must be proportionably free. Dorsal ribs only 
are here met with, but these being now move-_ 
ably articulated to the sides of the spinal co- 
lumn, and moreover acting at their opposit 
extremity upon the ventral scuta, perform th 
duties of internal legs, and being continued 
an unbroken series from the very atlas neal 
to the termination of the tail, it is not diffieu 
to imagine the numbers and complexity of th 
additional muscles now provided, to wield oj 
gans so numerous and important. 
In Lizards and in Birds the thorax assume 
its most complete state of developement, at 
exhibits both dorsal and sternal ribs articu 
to each other and capable of extensive move. 
ments ; muscles are therefore given to act upe 
both the dorsal and the sternal series. 
Lastly, in the mammiferous races the 
rior costal bones are once more removed, the 
place be.ng oncupted by elastic cartilages, 
resiliency of which to some extent antagoniz 
those muscles which act upon the mo 
portions of the thorax. 
The sternum, or rather the sternal syste 
bones, althouzh frequently found to ef 
largely into the composition of a thoracic | 
vity, seems rather to be in relation with 
anterior extremity, and the muscles der 
from it principa!ly subservient to the moti 
of those limbs. Thus in the frog and toad 
have a largely developed sternum without ei 
ribs or thorax; and in the case of Birds, 
strict correspondence between the conditic 
the sternum and the powers of flight is 
strikingly exemplified. a 
3. Perhaps the most interesting lesson to 
derived from such a survey of the museu 
system of vertebrate animals as this, is tat 
by an examination of the hyoid apparatus, 
of the musc'es connected with it, in the di 
rent members of the vertebrate series, and al: 
during the different phases of embryonic 
lopement, in any of, the air-breathing or | 
elevated classes. It is in Fishes that thi 
of the ske!etoa exhibits the greatest comph 
of structure, and forms a most elaborate ff 
work of branchial arches, destined to st 
the gills, which some writers have been tel 
erroneously to consider identical with the t 
of the air-breathing races. The branch 
hyoid organs are in fact substitutes for t 
racic or pulmonary portion of the sk 
and in exact proportion as the latter | 
more complete, and better adapted te 
respiration, does the former shrink in its 
sions and become simplified by the a 
of successive portions, which previously 
into its composition, and a consequent ret 
ling, as it were, of the muscles connected | 
with. Thus during the metamorphosis” 
tadpole, the branchial arches that before 
largely developed, are progressively foul 
disappear as the lungs assume their offic 
the whole hyoid system of bones and mi 
changed so as to become adapted to the 
formance of totally different functions. 
The permanent or adult condition of 
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