rill-: ISATRACFUA OF NORTH AMERICA. 



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the lorc'-K'j;.s arc thus external the hraiiehial chainbers reniiiiii iii free 

 eoiniiiuiiii'atioii witli the external niediinn by tlie .slit around the base 

 ol" eacli loK'-U'j;-. Tlicse soon elo.sc, however, and (lu^ skin of the fore- 

 h><i, is cut oir from that of the body adjacent by a distinct .scam, whicli 

 disai)|)ears hiter. This part of tlie (k'velopment of tiie iSalienlia is one 

 of the most remarliabk'i histories in the zooh)<iy of the vertebrata. 



The skin wliicli covers the fore limb of the advanced tadpole is not 

 a part of the true skin wliitih invests the body, sincte the branchial cav- 

 ity is inclosed lonj; bcfon^ the le;;' apjtears; but it ari.ses beneath the 

 mucous nuMnbrane which lint's the branchial chainbers. This anomaly 

 is perliai)s a case of rcvi-rsion. The. fore-lcj;s of primitive llatraehia 

 wen' no doubt external, as in salamanders, and they became iniilo.sed 

 by the growth of the opcrculuni like intej-unient in the larval Salientia. 

 A prolonjiation of tin; tadpole staj^e would result in a retardation of the 

 •jfrowth of the foreleg an<l an acceleration of that of the opereulum. 

 The urowtli of the trueskin of the inclosed rej>ion would bethus retarded 

 in the Ie;4' and atrophied in the wall of the chamber. (IMate 51, tij^s. 4-(»,) 



The shoulder yii'dle appears .separated from other parts of the skele- 

 ton, bctwei-n tlu' muscU's. The coraeoid and procoraeoid form a loop, 

 directe«l downwards and inwards, farremoved from that of the opposite 

 side, and present at this time an arciferous type in all forms of the order 

 .Salientia, (See (i;;. ."i!>.) 



The characu'is of the eartilajiinous skull of the larva' of the Salien- 

 tia are peculiar and veiy dillV-rent from those of the adult. The sus- 

 liensurium of the lower jaw is excee<linj;ly elongated forwards, so that 

 lor the purpose »»f securinj;' a lixed point for the lower jaw (represented 

 now by Meckt-rs carlilaf-e) it scuds upwards a proci'.ss near its anterior 

 extremity t(» tl. external an>;lesol the cartilaj^inous ethmoid, formingaii 

 ;u licnlation. It lli« ;i descends aj,'ain, and Meckel's cartilaj^e anicidates 

 freely with its extremity. Ti>ere is a curved (larlila^ic attache<l to the 

 extremity of each .Meckel's cartila.u:e (the t wti formin;;a half circle, oi>en- 

 inji foi wards), which t'orni the support of the lunctional lower lip in the 

 lar\a. These are the lower labial »ii sympli_\seid cai tilaj;es, ai>d are rep- 

 resented in the adult l»y a paii' of short bones of the same nanu' (men- 

 loiMcckcii.ins of Parker). Tlu' premaxillaiy bones are in like manner 

 rei»reM'nted by two carlila;:«'s, which are loosely uttached above to the 

 two ciurcspondin.ii' processes or i'oiinni of the trabecular cartilajjje, which 

 form the roof of the mu/zle in front (»f the etlnnoid. (Plate "»(►, fij>-. 2.) 

 The eeratoliyai is a robust bone, which articulates with the quailrate 

 cartila^ic Itclow tiu' orbit, contractinji' in diameter as it extends down- 

 wards and forwards. In the jtroce.ss of ji'rowth its articulation with the 

 • luadratc be«!omes more and more posterior, until it leaves that element 

 entirely, and comes in contaci. and in sonu' cases fuses, with the carti- 

 lai;e <»f the b;ise of the skull in front of the stapes and near the inter- 

 stapedial. (Plate .~»(l, fiLf. .i.) 



Jiesidcs the structuics (tf the larval hyoid apparatus already do- 



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