114 SHOULDER-GIRDLE AND BREAST-BONE. 



lip is longer than the right (fig. 4); the right upper lip is longer than the left (fig. 5). Tn 

 Trachydosaurm rugosus the first two cervical vertebrae are devoid of free ribs ; from the third 

 to the eighth (inclusive) there are floating ribs ; fig. 3 shows the lower part of the last and 

 penultimate cervicals ; and it is seen that they are (as in Lcemanctus and Cyclodus] as long as 

 the vertebral part of the dorsal ribs. There are, as in Cyclodus, three pairs of sternal ribs arti- 

 culated by perfect synovial joints with the vertebral ribs above, and with the large anterior 

 moiety of the Sternum below, so that this part is a " pra-mesosternum ;" and not a mere 

 " manubrium :" two more meso-sternal regions have been added by taking in the lower part 

 of the xiphisternal horns (figs. 3 and 4). We here have an additional help towards a proper 

 conception of the nature of these parts, for the metamorphosis has not gone to the same extent 

 as in the last instance, and the two moieties of the new meso-sternal piece are merely united 

 by an isthmus at each end. Moreover, the transverse semi-segmentation is at a further distance 

 from the mid-line, so that the structure is altogether looser and less finished than in Cyclodus. 

 Nevertheless, the two diverging horns, behind, articulating with the fifth thoracic ribs, are really 

 meso-sternal now; the notch between them is a primordial, posterior meso-sternal notch; and 

 there is no xiphisternal left by this morphological process. The ossification of the Sternum of 

 Trachydosaurm is by " endostosis ;" and this is symmetrical, as in all the Lacertians. The limb- 

 girdles themselves are only half as large in proportion to the body as in the Iguana ; for these 

 Scincoid Cyclodonts graduate, through intermediate species, to the "Atypical Squarnate 

 Saurians," namely, the Blind-worm, Glass-snake, &c. There is no semi-segmentation of the 

 costal arches, so as to produce "costae intermediae." 



Example 5. Psammosaurus scincus, Merrem. 



Plate X, figs. 7 and 8, show the Shoulder-girdle and Sternum of the Land-monitor of 

 Egypt, the Ouaran-el-hard of the Arabs : the figures are one-eighth larger than the real objects. 

 I shall now describe these structures in two members of the Varanian group, for they stand in 

 sharp contrast to those last under review, and yet I shall be able to show that there is no essential 

 difference in their morphology. The Monitors appear to me to be the noblest of the Lacertilia, 

 and assuredly the Cyclodonts are a long way down in the group : the former may be taken as 

 the type of their great Order ; for the Crocodiles, although nearer the Mammalia, are evidently 

 aberrant, and must be kept apart from the Lacertilia ; the Chamaeleons also are very aberrant 

 from the other Lizards. The Varanians have some characters in their skull which foreshadow 

 what is normal in the Bird-class, and this is in harmony with what is remarkable in the supra- 

 scapula of Psammosaurus (Plate X, fig. 7, s. sc.), namely, its obliquity, so greatly in contrast with 

 the regular, fan-like form seen in the Cyclodonts. It keeps its Lacertian character, however, in being 

 ossified only partially, and by its own endosteal layers : it is strongly constricted at its neck, 

 showing that it is really a ray superimposed upon the scapula, and not a mere process or crest of 

 that bone. Amongst the proper Lacertians Psammosaurus is peculiar in having its scapula 

 (sc.) entirely invested by the ectosteal layer ; in this it agrees with all the Amphibia ; with the 

 two-legged Amphisbaenian Chirotes ;. with the Chamaeleons and Crocodiles ; and with the Warm- 

 blooded Classes generally. If we compare this scapula with that of the Iguana and the Cyclodonts, 

 it is evident that the meso-scapula is connate with the scapula proper ; if we look at the next 

 instance (Plate X, fig. 9), it will be seen that the scapula shown in fig. 7 is altogether devoid of 



