208 CLASS XV. 



In tlie true serpents the sternum and the belt of the clavicles 

 are both wanting. In the frogs the sternum is as it were super- 

 seded by the two pairs of clavicles, which meet one another in 

 the mid-plane, and is almost limited to a triangular piece in front 

 of these and a stiliform piece behind them (the episternale and 

 xipJiisternale) , to both of which a thin round cartilaginous disc is 

 attached. In the sternum of the lizards a rhomboidal principal 

 piece is seen, and in front of it frequently a bone that runs out into 

 two transverse arms and a stiliform part behind, that extends over 

 the rhomboidal disc. Other small bony pieces may range them- 

 selves backwards, to which, as well as to the central rhomboid 

 piece, the ribs are attached at the sides. 



There are usually, as in birds, two clavicles on each side. The 

 anterior clavicles, which correspond to the furcula of birds, are 

 thin, and lie towards the anterior margin of the sternum; the 

 posterior clavicles are broader {ossa coraco'idea) and run obliquely 

 to the anterior side of the rhomboid piece of the sternum. If only 

 one pair of clavicles are present {crocodilus, chamceleon), it is the 

 anterior pair, those which correspond to the clavicles of mammals, 

 that are wanting. 



The pelvis of the frogs consists of two long iliac bones {pssa 

 ilea), which are fastened to strong and broad processes of the 

 •sacral vertebra, and meet behind at an acute angle the long tri- 

 angular compressed caudal vertebra lying between them. At the 



Observationes ad Anatomiam Cheloniormn. Berolini, 1838, 4to, Mueller's ArcTiiv, 

 1839, ^- '^9° — ^95- H. Rathke however declared himself against this view, and only- 

 regarded the marginal pieces of the dorsal shield, together with the whole thoracic 

 shield, as dermal skeleton ; Uehcr die Entwiclcelung der Schildkroten. Braunschweig, 



1848. This controversy was afterwards discussed hy R. OwEN, Phil. Transactions for 



1849, Part I. pp. 151 — 171, PI. 13, whose conclusions respecting it have princiimlly 

 formed the basis of the view we have presented. [The nine sternal pieces were named 

 by Geopfrot St. Hilaire as follows, a middle piece the entostemal, with 4 pairs of 

 pieces, viz. 2 episternals in front of entosternal, 1 hyosternals, a hyposternals, 2 xiphi- 

 sternals, one on each side from before backwards. "The entosternal, and perhaps 

 the episternals, are the sole parts of the plastron which can be referred to the sternum 

 . . . the parial or lateral parts, more especially the hyosternals and hyposternals, are the 

 true haemapophyses," (sternal and abdominal ribs) "but inconnation with dermal bony 

 plates to which their characteristic breadth, especially in the land and fresh-water 

 chelonians, is chiefly due." OwEN 1. 1. p. 166.] On the sternum of Saurians see 

 H. Eathke Ueber den Bau imd die Entwickelung des Brustbeins der Saurier. Konigs- 

 berg, 1853, 4to. 



