112 SHOULDER-GIRDLE AND BREAST-BONE. 



these parts in Cydodus nigroluteus, magnified one and a half diameter. The large fan-shaped 

 supra-scapula (fig. 1, sc.) is everywhere affected by endostosis ; and there is no distinction between 

 the bony core of the scapula and the supra-scapular bone-substance ; this ossification also runs 

 continuously down the marginal bar (p. sc.) ; and the lower cartilage (p. cr.) is similarly ossified ; 

 so that the prae-scapula, prae-coracoid, and epicoracoid, together form one half-bony band of con- 

 siderable breadth, especially below (see figs. 1 and 2, p. sc., p. cr., e. cr.). The heads of the scapula 

 (sc.) and coracoid (cr.) unite by suture, and at some distance below this suture is seen the nerve- 

 passage. As in the Iguana, the scapula is bifurcate above, the space between the forks being the 

 "scapular fenestra" (sc. f.); this is less than in the Iguana, and the forks are more nearly equal : the 

 lower fork, which runs upwards and forwards, is the meso-scapula or " acromion" (m. sc). Below 

 the meso-scapula is the coraco-scapular notch not fenestra ; and this is bounded below by the root 

 of the prse-coracoid (p. cr.) : the coracoid itself (cr.) is only bifurcate, and has a long fenestra (cr. f.) : 

 the epicoracoids (e. cr.) are very large, and overlap each other (fig. 2, e. cr.) ; they nearly rival those 

 of the Urodelous Amphibia. The splint-bones (cl., i. cl.) are relatively very large ; they are much 

 more splintery and lath-like than is usual in the Lacertilia, and the clavicles (cl.) are peculiarly 

 ichthyic. The cross-shaped inter-clavicle (fig. 2, i. cl.) must be compared with the plastron- 

 bones of the Chelonians (Plate XII) ; it is four-rayed, and the transverse rays are slightly 

 deflected, and are nearly equal to the fore-and-aft portions of the main or longitudinal part. 

 This latter part, both before and behind, is lancet-shaped, but the points are blunt : the great 

 transverse extension of the inter-clavicle is a correlate of the expansion of the epicoracoids. 



The Sternum (st.) in its main part is lozenge-shaped ; the four oblique sides being nearly 

 equal ; it is very flat, rather thin, and is continuous behind with the smaller piece : a constriction, 

 however, shows that transverse segmentation did commence, but was arrested. A primordial 

 notch (hidden in fig. 2 by the inter-clavicle) separates the deeply grooved coraco-sternal regions 

 (see this groove in fig. 1, st.). The left moiety is larger than the right (fig. 2), and these regions 

 are much thicker than the rest of the Sternum. Three pairs of ribs articulate by perfect joints 

 with the postero-lateral margins, so that in the main piece we have the manubrium and the next 

 two sternal pieces in a connate condition ; but the interspaces between the articular eminences are 

 well notched, showing a readiness for transverse cleavage of the continuous sternal mass. The 

 first pair of perfect ribs belong to the ninth vertebra ; the seventh and eighth cervicals have ribs 

 equal in size to the vertebral part of the first dorsal ; three vertebrae in front of these have small 

 free ribs, but the three foremost cervicals have no free ribs. The bifurcate xiphisternals, such 

 as we saw in the Iguana, have in this case undergone a further metamorphosis, and they are 

 now a^j//zsternal no longer, but wzesosternal. Being primarily in close apposition at the mid- 

 line save at their middle, the inner edges of these "horns" have coalesced, all except a fourth 

 part, which part lies nearly between the fourth pair of thoracic ribs ; this unclosed space is seen as 

 a tear-shaped " fontanelle" (fig. 2, st. f.). The fourth and fifth sternal ribs, with which this 

 part of the Sternum was continuous, have become nearly segmented off by transverse cleavage 

 (fig. 2) ; but there is a continuous pith of cartilage not severed in this growth-process, as also 

 there is between the two divisions of the Sternum. The fourth sternal rib (s. r. 4) is much 

 urther from the mid-line than the fifth, for the additional sternal piece is widest where this rib runs 

 into it ; and it is also twice as far from the third rib as that is from the second : the fourth and 

 fifth are at the normal distance. This unusual space between the third and fourth ribs, and the 

 incompleteness of the segmentation between the new key-stone and the pier of the fourth and 



