184 THE ANATOMY OF VERTEBRATED ANIMALS. 



hyoidean apparatus. No trace of any sclerotic ring has been 

 found. 



The teeth of the Plesiosauria are sharp-pointed, curved, 

 and the outer surfaces of their crowns striated. Each tooth 

 is lodged in a distinct alveolus, with which, as in the CrocO' 

 dilia, it does not become anchylosed. 



The pectoral arch (Fig. Q'^, E) is 'one of the most remark- 

 able parts of the organization of the Pleslosauria. It consists, 

 in the first place, of two very large coracoids, the long axes 

 of which are parallel with one another, while their inner edges 

 meet, without overlapping, throughout the greater part of 

 their extent. In this respect they differ from any of the 

 Lacertllla^ wdiich are provided with well-developed limbs. In 

 these the long axes of the coracoids always cut one another 

 at a large angle, open posteriorly — a circumstance which 

 results from the manner in which the coracoids are received 

 into grooves in the anterolateral edges of the rhomboidal part 

 of the sternum. Hence it would appear that the Pleslosauria^ 

 like the Chelonia, did not possess any thing corresponding to 

 this rhomboidal part of the sternum, but that the intercoracoid 

 part of the sternum was either absent, or reduced to a mere 

 band, as in some JBatrachia. 



The scapulae are unlike the corresponding organs in any 

 other reptile. Tlie glenoidal end, stout and strong, is con 

 tinned horizontally forward and inward, as a bony prism, with 

 a somewhat concave inner edge, and flat inferior surface. The 

 outer surface, rising up at right angles to the ventral surface, 

 gives rise to a well-defined edge; at a short distance from the 

 glenoidal end, the part of the bone which bears this surface is 

 produced upward and backward, into a low recurved plate. 

 This part appears to represent the proper body of the scapula 

 in other Reptiles, while the horizontal prolongation answers 

 to that preglenoidal process of the scapula, which extends 

 forward and inward as a free bony bar in many Lacertilia — 

 for example. Iguana. 



In well-preserved specimens, a broad hoop of substance 

 (Fig. 68, E, a), which seems to have been but imperfectly 

 ossified, extends across the middle line of the bod}^, from the 

 preglenoidal process of one scapula to that of the other, and is 

 continued backward in the middle line, to the junction of the 

 two coracoids. This corresponds very nearly in form and 

 position to the epicoracoidal ossifications of the Lacertilia^ 

 combined with the clavicles and interclavicles ; but I have 

 never been able to detect any distinct clavicular, or intercla- 



