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TIIH HATRACIIIA OF NORTH AMIUIICA. 



245 



identity between tlie two types it would only bo necessary to elongate 

 the ilia of the latter. The developed sternal apparatus and sliouhba' 

 fiirdle of th»', Salieutia is only found anionj; IJatrachian orders in the 

 JJhachitoMii anil Ste,uo(rei)ha!i. Thus in I'.ryops of the former there aic 

 clavicles, coraeoids, and episternuni (the last icdueed as in Trodela), 

 and iu Ai-tinodou there is also an epicdavicle ((iaudry). The ]>osterior 

 direction of the suspensoriuni of the lower Jaw of the Salieutia is also 

 oidy found in tiu' extinct orders named, pointinji- aj;ain to this origin. 

 In other recent orders these bones are directed forwards. 



Tlu^ in(»ditications ellected iu the Ilhaciiitonioiis skeleton to produce 

 the Saiientian, have been jiartly llu' same as those which have produced 

 the other existing orders, Tlius the triuMcrtebral centra have been re- 

 l)Iaced by complete iutercentra, and several ])osterior cranial bones have 

 been lost. The ilia have been greatly elongated, and in so doing have 

 embraced vertebra' siu-cessively niori^ and mor«' anteriorly, so that tlM^ 

 luinibcr bet w(-eu tiu ilia and the cranium has been greatly redutted, and 

 tlif vertebra' posterior to the i)oiid of attachment become atrophied iu 

 part and coiicrcsccnt iu i»ait. This jtro{!ess has been carried to the 

 greatest degree iu the extinct family of the raheobatraehida-. Here 

 thi^ ilia extend to two verrebra- in advance of the ninth or usual sacral, 

 tiiiis inclosing three vertebra' in the sacrum, and leaving only .s/.i' for 

 the remainder of the column. The coracoid is probably that of the 

 Stegoceplialons order, as it is better developed than iu the Uhachitomi. 

 The second row of the tarsus has also become icd need from these primi- 

 tiv«' types i»y atrophy, while the lirst low has been I'educcd to two boues. 

 as iu the M ammalia, w lii<'h have been greatly elongated. A jtarallel 

 caseoccuis in the Mammalia in somn lemurs, particularly in tiie Tar- 

 siida-. 



I have discovered that th«^ (lanocephala (Trimerorhachis), ami the 

 IMiachitoiiii (Tatrachys) possessed an <'Ioiigate coluau'lla auris, wiii(;h 

 is directed outwaids. backwards, and upwards to a- possible iiieiii- 

 Imniitin tjimpaiii, which may have occ.u|tied the notch external to the 

 OS inh rniliin .* ( Plate ,")(», tigs. 1-7.) 



The subdivision of this rod may have given origin to three of the 

 f.iur distiiu't cl«'iiiciitsexliil»ited by tin' Salieutia. (I'lates P.KoO.) The 

 homologies of these with the thr«'e j>rincipal osxicKht ^nitliliis \t^ \)nH>,\- 

 ble. Tile history of these parts shows tliat tlie biek of auditory <»ssieles 

 displayeil l»y some Salieutia and by all Urodela (IMates 4.S, 1!>) is the 

 residt of deg<'Ueracy. 



The cause of some of the modifications of the skeleton can Ite traced 

 tcMise. 'J'hus the coustaiil muscular stress on liie ilia iu humping the 

 back previous to leaping must have had a tenden(ry to draw it for- 

 wards not only on itself, but on its verteiiral atfaciinu'Uts, whi(!h are 

 (iartilaginons and yielding. 'I'he elongation of the lirst row of taisal 



•AiMcric.'iti Niitiinilist, l-'>s, !>. lCi."> : AiiictIchi .limriiiif of Moriiliolojry. Vnl. ii, I't. 

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