hyoid apparatus likewise undergoes a progres- 
sive simplification as we examine it in the more 
elevated forms of Vertebrata. Thus, in the 
bird it still consists of elements, that in the 
mammiferous animal may be dispensed with. 
The cornua, the last remnants of the branchial 
arches, are still largely developed in many qua- 
drapeds, and in fact it is only when we arrive 
at the human species that we see the pieces 
composing the byoid portion of the skeleton 
reduced to their simplest condition, and the 
muscles appended thereto correspondently re- 
duced in their number and modified as regards 
the functions they perform. 
4. The muscles that act upon the opercular 
Openings in Fishes are, of course, peculiar to 
_ animals possessed of a branchial respiratory 
system. 
5. The muscles of the limbs exhibit perhaps 
greater varieties than any others belonging to 
the animal economy, their existence and rela- 
tive size being entirely dependent upon the 
kind of progression conferred on any given race 
or family of the vertebrate creation. It would 
‘seem indeed that an inverse proportion always 
_ €xists between the condition of this system of 
“muscles and those that act upon the trank— 
_ the large developement of the one set rendering 
the other of secondary importance. Thus in 
the generality of the osseous Fishes the enor- 
mous bulk of the lateral muscles of the trunk 
renders any great strength of limb unnecessary, 
“and the muscles moving the pectoral and ven- 
tral fins, the representatives of the arms and 
legs, are proportionately small and feeble; but 
in the Plagiostome Cartilaginous Fishes, the 
_ Skates and Rays, the conditions are precisely 
reversed ; the muscles of the trunk shrink into 
“comparative insignificance, and the enormously 
‘developed hands, which here form the great 
__ bulk of the body, moved as they are by muscles 
__ 0f corresponding power, form the great agents 
__ in locomotion, and by their vigorous flappings 
_ Taise these creatures from the bottom of the 
_ Sea, their usual resting-place. 
___The phenomena attendant upon the growth 
of the limbs in Amphibious Reptiles beautifully 
exemplify the same circumstances. In the 
 Lepido-siren, that possesses still the form an‘ 
the Scales of a fish, although it breathes both 
ae gills and lungs, the legs or fins, for it is 
_ difficult to say to which appellation they are 
‘best entitled, are of the simplest possible struc- 
ture, each consisting but of a simple, tapering 
_ Stem, so flexible and feeble that it can scarcely 
be deemed at all useful for the purposes of 1o- 
comotion. 
____ Inthe Siren lacertina we have still the long 
and flexible body of an eel, the tail obviously 
\ forming the chief, or, indeed, the only effective 
__-4gentin progression. Nevertheless, seeing that 
is Amphibian being possessed of lungs can 
breathe the air, the first sproutings of legs are 
here manifest. Two rudimentary limbs corres- 
ponding with the anterior pair of other reptiles, 
and terminated by four extremely imperfect 
toes, are appended to a feeble scapulary appa- 
is, and thus the Siren is allowed to raise its 
head at least out of the, marsh where it re- 
i esl ee 
MUSCULAR SYSTEM. 
543 
sides, and obtain a supply of the atmospheric 
fluid. 
The Proteus is, in form, almost as fish-like 
as the Siren, and its tail is still a strong and 
muscular oar; the limbs nevertheless are slightly 
more developed ; and besides the imperfectante- 
rior extremities, each of which is terminated 
by three toes, a rudimentary pelvis and pelvic 
extremity are now sketched out, the latter pre- 
senting two little toes, but hardly as yet suffi- 
ciently complete to be useful as locomotive 
organs. 
Equally striking examples of the gradual de- 
velopement of locomotive extremities are found 
in those reptiles whereby the transition is effect- 
ed, between the Ophidian and Saurian types of 
structure ; thus in the genus Anguis, as for ex- 
ample, in the common English blind-worm 
( Anguis fragilis ), although externally it would 
appear to be as strictly apodous as the gene- 
rality of other serpents, yet on stripping off the 
skin, these reptiles are found to possess the first 
rudiments of limbs, that are afterwards to be 
made efficient in more highly gifted genera; a 
little pelvis 1s distinctly discermble, imbedded 
in the muscles towards the hinder part of the 
body ; and, in front, a sternum, scapula, and 
clavicle, may all be perceived hidden beneath 
the integument, although no traces of legs or 
feet are as yet to be detected. 
In other serpents more nearly approximated 
to the quadrupedal Saurians, as in the genus 
named Bimanes ( Chirotes, Cuv.) in additiou 
to the scapulary apparatus, two short anterior 
extremities armed with toes, moved by tole- 
rably complete muscles, are met with, whilst 
the hinder legs are wanting. In Bipes, on the 
contrary, it is the pelvic pair of legs that are 
developed, the place of the anterior being only 
indicated by the existence of the frame-work 
and muscles of the shoulder. Lastly, in the 
Saurians and Tortoises the quadrupedal type is 
fully adopted, and the muscles of the limbs 
assume an importance proportionate to the 
duties they have to perform. 
Still more interesting is it to watch the daily 
growth of the muscles that make their ap- 
pearance, as the legs of the Frog are slowly 
formed, budding, as it were, from the sides of 
the Tadpole, and vicariously taking the office 
of those, that previously constituted the loco- 
motive apparatus ; the vertebral system of mus- 
cles, whereby the tail of the aquatic animal 
is moved, being entirely obliterated as the limbs 
advance to maturity. 
6. The masticatory muscles, or those con- 
nected with those movements of the lower 
jaw that are concerned in the preparation of 
food, present great uniformity of arrangement 
throughout all the Vertebral orders, and ob- 
viously constitute a distinct and isolated group, 
the development of which is in exact relation 
with that of the rest of the manducatory ap- 
paratus. 
7. The tegumentary system of muscles, al- 
though only represented in the human body by 
a few detached and isolated remnants, con- 
stitutes among many of the lower animals a 
very important part of their economy, either 
