REPTILES. 97 



much as the main part of the Sternum, namely, by " sub-central endostosis." The short, ribless 

 sides are at first almost straight, and then they are concave as they narrow towards the meso- 

 sternum. The coracoid margins are thickened, as in Lizards generally, and then the prse-sternal plate 

 becomes thinner for the rest of its length. The meso-sternum (m. st.) is one line and four 

 fifths in length, its parallel moieties are each one tenth of a line in width ; they are a little enlarged 

 at each end, but on the whole they are very uniform bands ; they, like the prae-sternum, have no 

 ribs attached to them. 



The next division is composed of the " xiphisternals" (Plate VIII, fig. 8, x. st.) ; these are 

 of the same breadth, or nearly, as the meso-sternal bands, and they are one line and one fifth 

 in length ; they are somewhat clubbed where they join the meso-sternals, are greatly curved 

 outwards, the convex margin being behind or within, and their posterior free ends are clubbed 

 and rounded. The ossification of all the parts of the Sternum is evidently typically Lacertilian 

 it being "subcentral endostosis;" and what is more, the segmentation, transversely, into the 

 three typical regions, is by an arrested transverse cleaving; for here, as is so common in the lower 

 part of the costal arches of Lizards, there is a pith of cartilage not cut through by the natural 

 cleavage of the parts, and it is this which so long resists endostosis in this Class, lying as a 

 thin innermost plate of soft cartilage in flattened parts, and as a delicate rod surrounded by 

 bone (which bone itself has a bark of soft cartilage) in rounded rods. 



It is evident that J. Miiller's description, given by Rathke (transl., p. 91), gives the whole meso- 

 xiphisternum as one piece ; the xiphisternals, with the dried intervening membrane, forming the 

 broad end of the long triangular appendage to the shield-shaped manubrium ; it is possible that 

 these bands differ in different individuals, both as to relative length and as to the degree of 

 divergence of the xiphisternal horns. 



I shall have to refer to these structures of Chirotes several times before my descriptions are 

 finished. 



2. " SAURIA SQUAMATA ATYPICA." 

 Shoulder-girdle and Sternum both present. 



Example 1. Acontias meleagris, Linn., sp. See transl. of Rathke, p. 91. 

 Example 2. Ophisaurus ventralis, Linn., sp. See transl. of Rathke, p. 92. 

 Example 3. Pseudopus Pattasii, Cuv. See transl. of Rathke, p. 92. 

 Example 4. Anguis fragilis, Linn. 



Rathke's description of the Sternum of this species has already been given (p. 92) with those 

 of the other three instances ; but he treats of the inter- clavicle as part of the Sternum, and gives 

 no account of the Shoulder-girdle. We now come very close to the typical Lacertilia, and I have 

 been profuse of large illustrations of the Shoulder of this species, that I may be better prepared to 

 illustrate the more highly segmented, and more fully developed parts in the perfected Reptile. The 

 13 



