122 SHOULDER-GIRDLE AND BREAST-BONE. 



RATHKE, ' Brustbein der Saurier,' pp. 17, 18. 



XIII. The Sternum in the Chamseleonidse appears to be of simpler structure than, so far as 

 present observations show, in any of the remaining typical Scaly Reptiles. A portion of the skeleton 

 which corresponds to the anterior portion of the Sternum [inter-clavicle] of other Scaly Reptiles 

 wholly fails here. Their entire Sternum, indeed, consists only of one piece, which, to all appearance, 

 never ossifies, but always remains cartilaginous [in that case his specimens must have been very 

 young]. It is, moreover, in relation to the whole length of the body only of moderate length, and in 

 relation to its own length only of moderate breadth, though this varies in different parts. On the 

 whole, however, it has the form of a small table. Anteriorly, where it is broadest, there may be 

 observed two borders of equal length, which become continuous with one another at a rounded, obtuse 

 angle. These borders run outwards and backwards, and with these the hooked clavicle bones [cora- 

 coids] are connected, just as the same bones are connected to two similar borders of the posterior 

 sternal piece of other Reptiles. From these borders, especially in C/ianneleo vulgar is and Cham, 

 pumilus, to as far as about its posterior fourth, it becomes gradually smaller; then again it is some- 

 what broader, and finally, near its extremity, it is bevelled off like a chisel. The nick formed by and 

 at the extremity is sutured together by condensed connective tissue. A prolongation of this connective 

 tissue, proceeding from the centre, fills a short longitudinal fissure, which divides the posterior part of 

 the Sternum into two lateral halves, indicating a pair of horns. 



After what has been said it is obvious that we may thus differentiate two sections in the Sternum 

 of Chamseleons, an anterior and longer one, and a posterior and shorter one, the limits of each of 

 which are indicated by the smallest part of this part of the body, and of which the former may be 

 compared with the greater or anterior division [pra-meso-sternurri] of the posterior Sternal piece; 

 the latter, with the posterior division or to the asymmetrical appendage [xiphoid process] of the same 

 piece of the skeleton of other Scaly Reptiles. 



B. Shoulder-girdle without " Splint-bones." 



Example 1. Chamaeleo vulyaris, Dinneri!. 1 



My dissections of the common species of Chamseleon are figured in Plate XI, figs. 4 6, show- 

 ing the parts as magnified two and eight diameters. The Shoulder-girdle of the Chamseleon agrees 

 \vith that of Chirotcs (Plate VIII, figs. 8 10), and not with that of the more typical Lacertilia. 

 Each moiety (Plate XI, fig. 4) is nearly vertical in position, and is one continuous osseo- 

 cartilaginous piece. The supra-scapula (s. sc.) is of the usual form, but is relatively small; 

 it is entirely unossified, even in an old individual. The scapula (sc.) is a very narrow rod, 

 flattened, and curved backwards ; it is broad above, where it defines the supra-scapular region, 

 and below it is broader still ; the prse-scapular region is entirely deficient, and the meso-scapular 

 (m. sc.) is represented by the widened antero-inferior part ; the scapula is a perfect shaft-bone, 

 being entirely surrounded by the ectosteal sheath. The coracoid (cr.) is ossified in the same 

 manner, but it is imperfect, just reaching the scapula above, and having a perfectly soft " pra>" and 

 " epi-coracoid " continuous headland; the osseous laminae commenced on the posterior selvedge 



1 For an invaluable monograph of these aberrant Lacertians, I refer the reader to Dr. Gray's paper 

 ('Proc. Zool. Soc.,' 1864, part iii, pp. 465 479, pis. xxxi, xxxii). 



