REPTILES. 



In the frog, the nerves, which are to be tliftribiiti-d to 

 the arm, proceed from a very thick cord, which comes 

 from l)etwecn the fecoiid and tliird vertebrae : tliis makes 

 the lar^ell nerve in the whole body ; it is foon after joined 

 by a filament from the fucceeding pair, with which it in- 



regarded as the fciatic nerve. A great number of filament! 

 are afterwards detached from it to tlic mufcles : about the 

 middle and pofterior part it divides into two branches, 

 which pafs under the ham, and reprcfent the two popli- 

 teal nerves, the external and internal : thefe are afterwards 



timately unites ; this cord proceeds towards the axilla; it dillributed to the foot of the pofterior lee, nearly in the 

 fends ott a branch, which pafles above the Ihoulder, and is fame manner as to the human l(jot. 



loll in the mufcles of that part. The trunk continues its 

 courfe to the arm, and very foon forms two principal 

 brandies, and befides thefe, it alio fends iome filaments to 

 the extenfors of the fore-arm, and the articular capfule of 

 the head of the humerus. 



Of thefe two nervous cords, one is direfted forward 

 upon the humerus, and reprefents the median nerve ; it de- 

 taches fome filaments to the mufcles of the (kin. Arrived 

 at the fold of the fore-arm, the nerve plunges amongft the 

 mufcles, along with the tendon of the llerno-radialis, whicli 

 fupplies the place of the biceps ; it afterwards divides into 

 two branches, placed one above the other : tlic moll (lender 

 is fituated between the flexor mufcles of the fingers ; the 

 larger upon the furrow, which indicates the union of the 

 two bones of the fore-arm ; they pafs under the ligaments of 

 the carpus ; having reached the palm, the fuperiicial brancli 

 is loil in the (kin, which covers that part, and the deep- 

 leated is diltributed to each of the fingers, nearly as in 

 man. It alfo furniflies fome filaments to the mufcles of 

 the hand. 



The other cord reprefents the radial nerve ; it turns 

 round the humerus, and funiifhes, in the firil place, fome 

 branches to the exteiifor cubiti ; continuing to defcend 

 round the humerus, it arrives before the articulation v.ith 

 the bone of the fore -arm : it is aftorwards divided ; one of 



Great Sympalhctic Nervi. — There is no defcription of the 

 diftribiition of this nerve in reptiles, except in the mud 

 torloiff ; in wLich animal it was dillefted by Cuvier. It 

 is only dillindt in the interior of tiie back-fhell ; it ha« a 

 difpofition analogous to that of the cervical ganglion. The 

 pneumo-gailric nerve, however, adheres fo clofely to it, 

 that they cannot be feparated : we did not perceive any 

 filament on the neck, which could be regarded as the 

 trunk of the nerve. 



On the peritoneum, and on the bodies of the vertebra, 

 there appear very di(lir.6t nervous ganglia, which are mani- 

 feftly produced by tlie great (ympathetic. 



The ganglia are exactly fimilar to thofe of birds. There 

 are two fuperior and two inferior filaments, which pafs 

 under the tranfverfe procefs of the vertebra, that is united 

 to the back (hell : from the internal edge of each ganglion, 

 a (policlinic nerve proceeds, which forms a plexus round 

 each of the arteries produced by the aorta; one is alfo 

 fent to aliid in forming the pnlmuriary plexu^;. 



This nerve may be very eafily traced to the in 

 parts of the firfl vertebra of the tail. 



Pbyfiology of the Nervous Syjiem. --The obvious differences 

 of ftrufture between the warm-blooded animals and rep- 

 tiles, in this fyflem ; the exceedingly fmall brain and large 

 nerves of the latter, contralled with the (lender nerves and 



internal 



the branches is loll under the (kin, the other pad'es under large encephalon of the former, lead us to expeft no lefs 

 the back of the hand, and terminates on the convexity of (Iriking differences in their economy, than thofe which we 

 the fingers. From this defcription it will appear, that the actually difcover. Are we to explain by this difference 

 nerves of the arm in frogs very much refemble thofe of the httle influence that the brain exercifes over the other 

 the wing in birds. funftions, and the great individual and independent vitality, 

 In the falamaiider, the nerves of the arm are diftributed if we may ufe the expreflion, of the parts, which appear 

 as in the frog, but the brachial plexus is formed by two in fo many inflances in the amphibia ? The feverell in- 

 cervical, and two dorfal pairs, if we may regard as dorfal juries, which in man or the warm-blooded animals would 

 vertebra:, thofe which fuftain rudiments of the ribs. excite a fympathetic dilturbance of every fundtion, hicrhly 

 There are no brachial nerves in ferpents. dangerous, and in molt cafes fatal, are borne with little ap- 

 Ner-ves of the hind Limbs. — In hzards, there is only a parent fuffering, and rellored with facility. ( See the faiSts 

 fmall nervous filament, which proceeds from the femoral adduced in the phyiiology of the circulating fyftem to 

 nerve, and fupplies the phace of the obturator. The fe- prove the tenacity of life in this clafs.) Can we explain 



moral nerve is itfelf formed of the two laft lumbar pairs, 

 and pafles above the bones of the pelvis to be diltributed 

 in the mufcles of the anterior part of the thigh. The 

 fciatic nerve is produced by the three pairs of nerves, which 

 follow, and which alfo receive a filament from the laft lum- 

 bar pair ; the only cord they form proceeds along the in- 

 lide of the thigh, fubdividing in the mufcles, and extend- 

 ing to the toes. 



The diflribution of the nerves in the abdominal member 

 is nearly the fame in the falamander ; there are no differences, 



in the fame way the reprodudlive powers of this clafs f 

 Blumenbach feems to confider the explanation fufficient. 

 " The extraordinary (trength," fays he, " of the repro- 

 duAive power in feveral amphibia, and the aftonifhing 

 facility with which the procefs is carried on, muft be ex- 

 plained, if I miftake not, from the great magnitude of 

 their nerves, and the diminutive proportion of their brain. 

 The former parts are in confequence lets dependent on the 

 latter ; hence the whole machine has lefs powers of motion 

 and difplays lefs fympathy : the mode of exiftence is more 



except in the manner in which the plexus is formed. The fimple, and approaches more nearly to that of the vegetable 



femoral is produced by a fingle lumbar pair, which tranf- world, than in the warm-blooded claffes : but, on the con- 



mits a branch to the fciatic plexus, formed by the two trary, the pa 'ts poffefs a greater individual independent 



fucceeding pairs. vitality. Since, in confequence of this latter endowment, 



In the frog, three pairs of nerves enter into the compo- ftimuli, which operate on one part, or one fyftem, do not 



fition of the femoral plexus, before which they run the immediately affeft the whole frame by fympathy, as in 



whole length of the offa ilii, which are very long : when warm-blooded animals, we are enabled to explain the pecu- 



arrived at the thigh, the plexus fends off a nerve, which liar tenacity of fife, which is dilplayed under various cir- 



correfponds to the anterior femoral ; it is diftributed in cumllances in this clafs ; vi-:.. frogs continue tojump about 



radiated filaments to the fore part of the thigh. The relt after their heart has been torn out ; and tortoifes have lived 



of the plexus proceeds into the pelvis, and forms a large cord, for months after the removal of the whole brain from the 



which pafles to the pofterior part of the thigh, and may be cranium. The long continued power ot motion in partj 



5 E 2 virhich 



