116 SHOULDER-GIRDLE AND BREAST BONE. 



moieties coalesced more or less, instead of being arrested where we see them, that is, free behind, 

 and only joined in front. 



For such sternal horns, where the arrest renders their character doubtful, the term 

 " xiphisternals" may be used ; the additional epithet free being added where, as in Stellio, they 

 are further metamorphosed by being longitudinally cloven from the sternal ribs. There is a 

 partial differentiation of the " costa intermedia" from the sternal rib, the "endostosis" being 

 distinct, and leaving a narrow tract unossified (fig. 7, c. i., c. s.). 



Example 6. Monitor draccena, Linn., sp. 



My specimen (preserved in spirits) of this beautiful Varanian is fifteen inches long six for the 

 head and body, and nine for the tail. The figures in Plate X, 9 and 10, are magnified three 

 diameters. The differences between this and the last make me very desirous of working out a 

 large number of Lacertian genera ; but there is not room in the present Memoir for more than I 

 am giving; and I have taken care to display the structure of a sufficient number for the illus- 

 tration of the great group itself the Lacertilia ; and, what is of still greater importance, the 

 Vertebrata generally. The supra-scapula (fig. 9, s. sc.) is much broader and also more sym- 

 metrical than that of the last instance : it is an axe-blade, narrowing but little towards its back, 

 here represented by the lower margin. It is too large for the scapula, to which it forms a crest, 

 surmounting the shaft-bone beneath, and ending postero-inferiorly in a produced angle. The 

 two internal, sub-central bony plates are surrounded entirely by a selvedge of soft cartilage ; even 

 over the scapula the ossification is arrested so as to keep it distinct from the medullary bone of 

 that segment. The scapula (fig. 9, sc.) is in its main part like that of Psammosaurus, being a broad 

 phalangoid ray, with concave sides and convex ends ; the upper being the broadest, whilst the lower 

 is oblique. This bar contains in it the " meso-sternum," or acromion ; but, as in the last instance, 

 there has been no cleavage from the main ray : contrary to the last, however, there is there a prse- 

 scapula (fig. 9, p. sc.), and it is almost cleft from the main bar (sc.), the fenestra (c. .s. f.) being 

 long, narrow, and pointed above. The prse-scapular bar is entirely unossified, and this soft 

 condition is continued in front of the prse- coracoid root down to the angle (less than a right 

 angle) at which the prse-coracoid turns where it thickens, becomes semi-osseous, and passes into 

 the epicoracoid (e. cr.). This prae-scapular bar is an anterior continuation of the unossified cartilage 

 at the base of the supra-scapula, and it shows how that the segmentation is imperfect throughout 

 in the Lacertilia ; the cartilage, where it suffers fission, " cleaves the cleft " imperfectly, and the' 

 morphological regions for the most part are indicated by histological modifications. This 

 coraco-scapular fenestra will turn up again in the Sloths, and in the larger Ant-eaters among the 

 Mammalia ; but the fenestra which separates the " meso-scapula " from the " post-scapula " in 

 the Iguana and in the Cyclodonts will reappear in the Pangolins ; in the Batrachia we have the 

 lower part of this latter cleft ; in the Pangolins, the middle ; and in the Iguana and Cyclodonts, 

 the upper part ; in none of these is it perfect. We shall find an instance, however, of a complete 

 cleft between the pra3-scapula and the meso-post-scapula : that will turn up in the Cat-tribe, and 

 in allied forms. 



If the scapula of Monitor draceena is a key to the true morphology of the Mammalian 

 scapula, so also is its coracoid to that of the Bird ; for here we have again, as in the Iguana 

 and in Psammosaurus, the broad coracoid (cr.) sending forwards and downwards two broad 



