58 SHOULDER-GIRDLE AND BREAST-BONE. 



AMPHIBIA. 



GENERAL REMARKS. 



IN passing from the Fish-class to the Amphibians, the Proteus meets us at the very outset 

 with a grade of development very little above what is to be found in the Fishes. Indeed, the 

 whole group of Amphibians are so simple in their early embryonic development, that some 

 anatomists propose to class them, together with the Fishes, as one group the " Ichthyopsida." 



And yet the paternity of this Sub-reptilian group can be charged upon no particular 

 Order of Fishes ; their nearest relatives are to be found amongst the generalised types, such 

 as the Plagiostomes, the Sturgeons, and Lepidosiren. 



They all agree with the two latter types, and with Osseous Fishes generally, in having only 

 (as a rule) two or three vertebrae that can fairly be called cervical ; for the apex of the supra- 

 scapula in the Frog, as well as in Proteus, is, in its first appearance, in relation with the second 

 " intercentrum," or between the second and third vertebrae, exactly as in the Cod-fish. 



The most snake-like of the Amphibians, namely the Caecilians, do not possess such accessory 

 parts of the skeleton as limbs, or even limb-roots, at least as far as my opportunities for dissection 

 have gone. My subject was the Epicrium glutinosum, from Ceylon. 1 In all those Amphibians in 

 which metamorphosis does not affect the tail (Amphibia Urodela) the ossific process is much more 

 arrested than in the Anoura \ but in none of them is there any correlation of dermal bones to 

 the Shoulder-girdle; on the skull there is such a coexistence of both species of bone; -but not to 

 the same extent as has been described ; the supposed splints of the lower jaw being, in reality, 

 " ectostoses." 



In the Urodela by far the greater part of the Shoulder-girdle, and all the Sternum 

 (which is developed in most of the genera), continues totally unossified throughout life, whilst 

 the " endostosis" which is set up within each ectosteal sheath is not quite coextensive with 

 the outer layer of bone, and can only be seen in sections. Moreover, the " ectostoses" are arrested, 

 so that they only cover part of the territories to which they belong ; and in certain genera only 

 one or two of these bony patches are developed. 



"AMPHIBIA URODELA." 



A. With one Ossification in each moiety of the Shoulder-girdle. 

 Example 1. Proteus anguinus, Laurenti. 

 My specimen of Proteus* measures eight and a half inches from end to end ; and the figures 



1 The gift of Dr. Giinther. 



" This, with two fine Axolotls, and several other valuable specimens, I have received from 

 Mr. Edmund Christy ; they belonged originally to his late lamented brother, Mr. Henry Christy. 



