544 



MYRIAPODA. 



destined to act upon the skin itself or upon 

 cuticular structures of very diversified shape, 

 which are occasionally developed in different 

 regions of the body, and not (infrequently ap- 

 propriated to the performance of important 

 duties. In those quadrupeds that have their 

 backs covered with strong spines, such as the 

 Echidna, the Porcupine, and the Hedgehog, 

 the cutaneous muscles, usually named panni- 

 culus carnosus, are met with in their most com- 

 plete form, since in these creatures every quill 

 or spine is moved by muscular bands con- 

 nected with its base, that serve to erect or de- 

 press it at pleasure. The crests and other 

 moveable appendages to the skin met with 

 among Birds, are equally furnished with the 

 means of motion by strengthening particular 

 parts of the muscular apparatus in question. 



In Reptiles, on account of the nature of their 

 corneous integument, the muscles of the skin 

 are but slightly developed, or indeed most 

 generally are not to be detected. But in Fishes 

 they once more present themselves, under a 

 novel and most important aspect. The azygos 

 fins in these aquatic Vertebrata are, as is else- 

 where shewn (vide PISCES), derivations from the 

 exo-skeleton, and consequently all the slips of 

 muscle, that act upon the individual rays of 

 the dorsal, caudal, or anal fins, however ano- 

 malous their nature may appear without such 

 a key to their real character, are obviously 

 merely portions of the tegumentary system of 

 muscles here elevated into an importance not 

 witnessed in other animals, where the exo- 

 skeleton is less decidedly appropriated to the 

 purposes of locomotion. 



8. The muscles whereby vocal sounds are 

 modulated, are equally entitled to be looked 

 upon as a distinct and superadded system only 

 conferred upon certain races of Vertebrata, and 

 that under very various conditions. In Fishes 

 these muscles are of course absolutely wanting, 

 and even amongst the air-breathing Reptiles 

 they are so imperfectly developed as scarcely 

 to be regarded as vocal organs. But in Birds 

 and Mammalia they assume a higher form, and 

 are variously located and more or less nume- 

 rous in exact proportion as the voice is per- 

 fected. In Birds, indeed, the vocal muscles 

 are principally placed at the thoracic extremity 

 of the trachea, but in Quadrupeds and in Man, 

 at the opposite end, the whole machinery being 

 thus so completely altered that even analogies 

 between the different sets of muscles are not 

 easily pointed out. 



9. The diaphragm is an apparatus exclu- 

 sively conferred upon the Mammiferous Ver- 

 tebrata, since in these only is the thoracic 

 cavity separated from the abdomen by a mus- 

 cular septum. 



10. The muscles of the tongue must like- 

 wise be regarded as forming a distinct group, 

 increasing in complexity and extent of motion, 

 in proportion as the organ to which they belong 

 assumes greater importance, either as an in- 

 strument for the prehension of food, or as an 

 agent in mastication. 



11. The ocular system of muscles maybe 

 divided into those which act on the eyeball, 



and those employed in moving the palpebral 

 appendages. The former when complete con- 

 sist of four recti, two obliqui, and the choanoid 

 or suspensary muscle, which not unfrequently 

 is distinctly divided into four. The recti are 

 invariably met with and present few variations 

 worthy of notice. The obliquus superior in 

 Mammals passes through a pulley, which is 

 not the case in other Vertebrata, while the 

 choanoid muscle is principally met with in 

 Quadrupeds. 



The muscles of the eyelids are most per- 

 fectly developed in Birds, in which distinct 

 muscles are appropriated to the movements of 

 the upper and lower eyelid as well as to the 

 nictitating membrane, which in the feathered 

 races has a proper set of muscles appointed 

 to draw it over the eye not met with in other 

 classes. 



12. The muscles of the auditory apparatus 

 become fully developed only in the mammife- 

 rous ear, where four little muscles are inva- 

 riably found connected with the ossicula audi- 

 tus, as in the human subject. The muscles 

 appointed for the movements of the external 

 ear are, however, in many Quadrupeds much 

 more numerous than in Man ; in fact, in the 

 human ear they merely exist, in a rudimentary 

 condition. 



13. The nasal apparatus has likewise a sys- 

 tem of muscles of its own, although the in- 

 stances in which it is met with in anything 

 like a complete state of developement are com- 

 paratively rare. In Fishes, Reptiles, and Birds 

 these muscles, indeed, can hardly be said to 

 exist; and even in the generality of Mammals 

 they are feeble and unimportant. It is only in 

 the proboscidean species, that the nasal muscles 

 assume their full complexity, and the trunk of 

 the elephant is in modern times the only ex- 

 ample, wherein the anatomist can contemplate 

 them. 



14. The muscles of the generative system 

 are only found to exist, as a distinct set, in the 

 Mammalia, as in these alone is the urethral 

 canal complete, and a perfect ejaculatory ap- 

 paratus given. 



Thus, therefore, we may learn from this short 

 survey, that so far from finding in the human 

 frame the fullest and most elaborately con- 

 structed examples of the various divisions of 

 the muscular system, or, in other words, a ty- 

 pical condition of that part of the animal 

 economy, the human anatomist, in many in- 

 stances, has only an opportunity of examining 

 the vestiges or rudiments of organs, that in the 

 lower animals attain to a far more complete 

 developement. 



( T. Rt/mer Jones.) 



MYRIAPODA, (from the Greek //.t^.aj, 

 ten thousand, i. e. numerous, and irov<;, a foot,) 

 the name of an important and highly interest- 

 ing class of articulated animals, intermediate 

 in their structure and appearance between 

 the Annelidans and the Insecta, properly 

 so called ; approximating the former in the 

 worm-like form of their bodies, which are 

 composed of a great number of rings or seg- 



