MUSCULAR SYSTEM. 



543 



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 

 marnmiferous animal may be dispensed with. 

 The cornua, the last remnants of the branchial 

 arches, are still largely developed in many qua- 

 drupeds, and in fact it is only when we arrive 

 at the human species that we see the pieces 

 composing the hyoid 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 

 exists between the condition of this system of 

 muscles and those that act upon the trunk 

 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 

 of corresponding power, form the great agents 

 in locomotion, and by their vigorous flappings 

 raise 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 and 

 the scales of a fish, although it breathes both 

 with 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 lo- 

 comotion. 



In the Siren lacertina we have still the long 

 and flexible body of an eel, the tail obviously 

 forming the chief, or, indeed, the only effective 

 agent in progression. Nevertheless, seeing that 

 this 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- 

 ratus, and thus the Siren is allowed to raise its 

 head at least out of the marsh where it re- 



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 imperfect ante- 

 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 Jragilis), 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 is distinctly discernible, 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 addition 

 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 slosvly 

 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 



