In the Carnivorous CEPH A LOPODA 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 CEPHALOPODA.) Arrived at the vertebrate division of the ani mal 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 theframe work of the body, and must be regarded as entering into the composition of several dis tinct 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 poses, 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 he most elaborate and complex in their structure, are not unfre quently either wholly or partially obliterated, as we ascend the scale of animal life, and others equally important to the animals possessed of them, are only met with in certain races, that are endowed with peculiar habits or capabi lities.
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 sertions of every muscle, that lie 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 development.
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 vertebrae.
2. Costal system, muscles moving the ribs and parietes of the thorax and abdomen.
3. Hyoid system, muscles acting upon the os hyoides and branchial arches.
4. Opercnlar system, muscles moving the operculum of fishes.
5. Illuscles vibe 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 deal 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 exoskeleton. The muscles destined to act upon the flexible spine of the fish are propor tionate to the violence of the impulse required in moving 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 eggs.
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 condition 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.