In the Preropop Mo tusca, we likewise 
find the entire body enclosed in a muscular 
bag, forming what is called the visceral sac, 
but the locomotive organs present themselves 
under a different aspect. These consist of two 
muscular flaps or wings, appended to the op- 
posite sides of the neck, which form, in fact, 
two oars or paddles, wherewith the little Ptero- 
pods row themselves about from place to place, 
or gambol gaily among the waves, which some- 
times, in the northern oceans, swarm with count- 
less multitudes of them. The lateral fins in ques- 
tion were regarded by Cuvier as being likewise 
subservient to respiration, an opinion, however, 
which Eschricht satisfactorily confutes. The lat- 
ter writer, moreover, points out a little circum- 
Stance worth recording, namely, that the wings 
are not distinct and separate organs as at first 
they would appear, but that the muscles mov- 
ing them pass continuously in a crucial di- 
rection through the neck of the animal from 
one wing to the opposite, so as to convert the 
whole apparatus into an exact representation of 
the double paddle used by the Greenlander, in 
rowing his Bisi. or canoe, over the very seas 
frequented by the Pteropods, in such abun- 
dance. 
~ In the Carnivorous Cepuatopopa the mus- 
cular sac composing the body, the parietes of 
the head, and the long and flexible arms with 
their curiously constructed sucking cups ap- 
pended, are all made up of variously disposed 
‘contractile fibres; but these are too fully and 
“well described in another place to require more 
than a passing notice in this general survey. 
(See Cepuaropopa.) 
_ Arrived at the vertebrate division of the ani- 
_ tal series, we at once find the moving powers 
‘assuming a complexity of arrangement and 
Precision of action, proportional to the elabo- 
rate construction of the internal osseous, or car- 
__tilaginous skeleton, which now forms the frame- 
work of the body, and must be regarded as 
entering into the composition of several dis- 
_ tinet systems of organs appointed to different 
_ offices, and physiologically independent of 
each other. Each of these systems, or sets of 
muscles, indeed, is developed for special pur- 
goses, and so far are they from_ progres- 
sively presenting themselves, in a gradually 
‘Improving condition, as we rise from’ lower to 
‘more elevated orders of Vertebrate animals, 
_ that the physiologist must be prepared to ex- 
‘pect every irregularity in this respect ; impor- 
_ tant organs, or sets of organs, that in the lowest 
‘Vertebrata are found to be most elaborate and 
_ complex in their structure, are not unfre- 
“quently either wholly or partia!ly obliterated, as 
Be ascend the scale of animal life, and others 
_ equally important to the animals possessed of 
ben, are only met with in certain races, that 
are endowed with peculiar habits or capabi- 
ities. 
_ But, what is still more startling to the ana- 
tomist, who has confined his dissections to the 
‘examination of the muscular system as it exists 
in mature or complete animals, and has con- 
sequently been accustomed to describe as being 
permanent and invariable the origins and in- 
MUSCULAR SYSTEM. 
541 
sertions of every muscle, that he meets with, 
the study of embryogeny reveals to the philo- 
sophical enquirer a series of changes in pro- 
gress, as relates to the arrangement or even the 
existence of various parts of the animal eco- 
nomy, involving changes as remarkable, in all 
the muscular apparatus connected therewith. 
In order, therefore, fully to lay before the 
reader, with as much brevity as perspicuity 
will allow, phenomena so important as those 
which next offer themselves to our notice, it 
will be advisable, first, to enumerate the prin- 
cipal systems of muscles that enter into the 
composition of a completely formed Vertebrate 
creature, premising that each may be but feebly 
developed in proportion to the rest, and many 
of them, indeed, absolutely wanting in a given 
animal, and afterwards to examine separately 
the varieties of arrangement met with in the 
animal series in relation to each, and likewise 
the metamorphoses that accompany embryonic 
developmeut. 
Without overburdening with detail this in- 
teresting enquiry, or unnecessarily multiplying 
divisions of the muscular apparatus, we shall 
content ourselves with grouping all the muscles 
of a Vertebrate animal, as belonging to one or 
other of the following systems, each of which 
will demand separate examination. 
1. Vertebral system, muscles directly acting 
upon the spine and cranial vertebra. 
2. Cos‘al system, muscles moving the ribs 
and parietes of the thorax and abdomen. 
3. Hyvid system, muscles acting upon the 
os hyoides and branchial arches. 
4. Opercular system, muscles moving the 
operculum of fishes. 
5. Muscles of the limbs. 
6: Muscles acting upon the lower jaw and 
serving for mastication. 
7. Tegumentary system, muscles acting upon 
the skin and its appendages. 
8. Vocal system, muscles of the voice. 
9. Diaphragm. 
10. Lingual system. 
11. Ocular system, muscles moving the eye- 
ball and its appendages. 
12. Aural system, muscles acting upon the 
ossicles of hearing and moving the external ear. 
13. Nasal system, muscles acting upon 
moveable parts of the nose. 
14. Generative system, muscles attached to 
the apparatus of generation. 
1, The muscular apparatus peculiarly appro- 
priated to the movements of the vertebral chain 
of bones presents its maximum of developement 
in the osseous fishes, in which animals loco- 
motion being principally accomplished by the 
lateral sweepings of the broadly expanded ver- 
tical tail, every arrangement has been made to 
increase the depth of the spinal column and to 
extend the surface presented by the superior 
and inferior spinous processes to the greatest 
possible degree, not only by lengthening inor- 
dinately those processes themselves, but like- 
wise by appending to their extremities addi- 
tional pieces derived apparently from the 
exo-skeleton. The muscles destined to act 
upon the dexible spine of the fish are propor- 
