REPTILES. 121 



coalesced at the mid-line (see fig. 2), the ossific process being unusually active in this 

 Lizard. 



The " xiphisternal horns" (figs. 1 and 2, x. st.) are of extraordinary size, being more 

 than twice the length of the unusually large Sternum . they are scythe-shaped, increase in 

 breadth to the commencement of the last third, and then grow gradually to a'rather sharp point ; 

 their direction is backwards, upwards, and a little outwards. These long " horns " have their 

 own internal ossification, and there is a constricted isthmus of soft cartilage between these and 

 the sternal angles ; this constriction is an arrested transverse cleft. Such " horns " as these 

 reappear in the Mammalian Manis longicauda, &c., and in the Bird-class their nearest counter- 

 parts are seen in the Tinamou. 



The " costa intermedia " is well seen in Stellio (see Plate XI, fig. 6, where the first of these 

 is shown as magnified eight diameters). The vertebral rib (v. r. 1) has an epiphysis, then the 

 cartilage itself is constricted an arrested transverse deft, and at the eighth of an inch lower down 

 another constriction appears; between these there is an "endosteal" mass of bone (i. r. 1), then 

 below the lowest constriction we see the sternal rib (s. r. 1), which has its own internal ossification. 

 Altogether, the Stellio Lizard has many most important morphological characters, the first outlines 

 of things not clearly seen as yet, but which in due time manifest themselves in the Warm-blooded 

 Classes. 



Example 9. Polychrus marmoratus, Linn., sp. 



This Lizard is introduced here because of its correspondence in a very important character to 

 the Chamseleons, which come next after the more typical Lizards. In a half-grown specimen of 

 Polychrus marmoratus I find the main part of the Sternum lozenge-shaped, and having two pairs 

 of ribs articulated to its postero-lateral edges. At a short distance behind the second pair of 

 ribs the Sternum is constricted, it then becomes narrow, and has parallel edges, and this 

 narrow part is composed of two halves not much coalesced together, indeed entirely distinct in 

 their hinder half. The third pair of thoracic ribs are only partially segmented from the middle 

 of this narrow piece, and the fourth pair are continuous with its halves behind, bending outwards 

 from it at an obtuse angle ; this is exactly intermediate, morphologically, between what has been 

 described in the Iguana and the Cyclodonts (see Plates IX and X). The next nine costal 

 arches meet and coalesce below, each arch forming a small, triangular plate at the junction of 

 the right and left ribs; these plates are rudimentary "nieta-sternals." In this specimen there is 

 no separate ossification for this mesial part, but I shall presently show such a deposit in the 

 " meta-sternal " of the Chamseleon. The tenth abdominal ribs are small, and do not even meet 

 at the mid-line ; they are a long distance from their own vertebral segment. The ninth " abdo- 

 minal " ribs also are separated considerably from the vertebral parts of the arch. 



We now come to the Chamseleons, in which there is an entire absence of the Shoulder- 

 splints ; but before giving the result of my own observations, I will insert those of Rathke. 

 These are especially interesting, as in both Chamaeleo vulgaris and C. pumila his descriptions 

 indicate a much lower morphological stage than those dissected by me. 

 16 



