WEALDEN DINOSAURS. 



363 



Bones of the Extremities. — Scapular arch. 



The scapula of the Hylseosaurus (PI. 35, 51, and PI. 6) is longer and narrower than 

 in the Monitors and Iguanas, adhering in this respect to the Crocodilian t)'pe, but 

 most resembling in the shape of its blade or body, that of the genus Scincus. It 

 differs, however, from the scapulae of all known reptiles, and indicates an approach to 

 the Mammalian type, by the production of a strong obtuse acromial ridge, separated by 

 a deep and wide groove from the humeral and coracoid articular surfaces. The blade 

 of the scapula is long, flattened, slightly convex on the inner and proportionally 

 concave on the outer surface : the anterior margin is convex, the posterior one 

 concave ; the upper extremity or base truncate, slightly convex, with the posterior 

 angle a little produced, the anterior angle rounded off. On the outer side of the 

 scapula two broad convex ridges descend and converge to form the beginning of a thick 

 and strong spine, at fourteen inches distance from the base ; this then expands into the 

 thick acromial ridge, which extends transversely, and is continued forwards as a long 

 subprismatic process from the anterior angle of the head of the scapula. This process, 

 the homologue of which exists in the scapula of the Iguanodon, and more developed 

 in that of the Megalosaurus, is broken off in the present specimen about four inches 

 from the neck of the scapula, with which it forms a right angle. The acromion is 

 perforated at the base of its anterior prolongation by a foramen analogous to the 

 supraspinal one in the scapula of the Edentate Mammalia. Besides the scapulag 

 preserved in the connected part of the skeleton, there is, in the Mantellian Museum, a 

 nearly entire and detached scapula of larger size, discovered, in connection with many 

 other bones of the skeleton, in a layer of blue clay near Bolney, in Sussex, and indi- 

 cating the connected part of the skeleton first discovered in 1832 to have belonged to 

 an immature individual. The dimensions of this scapula are as follows : 



Length of tlie scapula 

 Breadth of its base 

 Breadth of its neck 

 Thickness of its base . 

 Thickness of its neck . 

 Breadth of subacromial groove 

 Breadth of humeral articulation 

 Breadth of coracoid articulation 



The coracoids, PI. 35, 52, present a much more simple form than in the Megalosau- 

 rus, and resemble those of the Scink and Chameleon, thus deviating in their great 

 breadth, like the coracoids of the Enaliosaurs, from the Crocodilian type. In the 



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