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TIIK HATUACllIA Ol' NOlii'H AMKUICA. 



23;j 



Vertebral bodies mulividod, separate proatlas wantiii};. Vertubne 

 very lew, on account of the anterior attaclnnent of the pelvis and the 

 disappearance of some and fusion into a sin^^le styloid bone (the uro- 

 style) of others of the vertebne posterior to the point of iittachment. 

 Ribs very short or ^vantiIl{,^ 



Coracoid, clavicle, and scupula osseous, well developed ; procoracoid, 

 epicoracoid, and suprascapula cartilaginous. Sternum present, entirely 

 posterior to the coracoids. No iMiesternuni nor interclavicle, but fro- 

 (luently a median element anterior to the clavicles called the omoster 

 num. 



I'elvis consisting' of the usual three elements, the inferior pairs closely 

 united, forminjjf a compressed body witliout obturator foramina. Ilium 

 subcylindric, very elonj^ate. 



Humerus without distinct head proxinuilly, but with an epipbysis. 

 Distally a globular condyle. Other long bones with epiphyses at both 

 extremities. Astragalus and calcanenm elongate, forming a limb seg- 

 ment. Carpal bones well developed, some of them, es[>ecially of the 

 distal series, contiuent. Tarsals of tlie distal series much reduced in 

 size and numl)ers. (I'hites 47, aK, etc.) 



Tlie auditory appendnges dill'er from those of the Urodela, Proteida, 

 and Trachystomata in tiieir greater (-omplexity. There is a cavum 

 tymi)ani or external ear and a series of ossicles and cartihiges extend- 

 ing througli it, structures all wanting to tlie orders nu^ntioned. The 

 stapes is, lilie tliat of thos(^ orders, an oval disk, which has no continu 

 ous process, but gives origin at its middle to the stapedius muscle. 

 Immediately in front of it tliere arises an osseous rod, the interstapedial 

 bone. Its base is cartilaginous, and is expanded with concave surface 

 lilting the convex surface of the skull. This rod terminates at tiie su- 

 perior interrujition of a Hat annular carlilage {Annidus tijmptoiicus), 

 which lies on the (piadrate cai'lilage and over the comjavity formed by 

 its forwards tiexure. The mesostapedial cartilage is attached by a point 

 on its interior face to the apex of the interstapedial, somewhat as an 

 anther of a llower is attached to its tilament. Its superior portion is 

 shorter, and is c(Minected with the «iiiadrate above by the mesostapedial 

 liganu'iit. Its inferior portion is more or less ex[)anded distally. Its 

 external face is Hat, and is applied to the inner side of the disciform 

 e[tistai>edial. The latter is api»lied like a lid to the annular cartilage 

 already mentioned. The mesostapedial then occupies a i)lace between 

 the annular and (he epistapedial cartilages. The niembranum tympani 

 tits closely over the latter. ( Plates 49-50.) 



The hyoid apparatus dilfers materially from that of the orders men- 

 tioned. It can only be understood by reference to its developnu'iit 

 from the larval stages. There are jiresent in the larva a ceratohyal 

 on each side and a first basibranchi il, as in Urodela. The hypohyal is 

 connate with the former. Posterior to the basibrancbial, two lateral 

 eartilagiuous plates, the " hyobranchials," meet on the middle line. 



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