180 PAJLEONTOLOGY 



gigas. The ento-stemal element is the only endo-skeletal | 

 uncombined with a dermal ossification in most Chelonia. The 

 epi-stemal, like the hyo- and hypo-sternals, appear to be abdo- 

 minal ribs, with superadded dermal ossifications in Ghelunia. 



The scapula? (fig. 65, 51) are instructively exhibited in the 

 very young specimen of the Archegosawrus figured in t. xiv., 

 fig. 4, of Von Meyer's treatise. The coracoids being doubtless 

 wholly cartilaginous at that stage, are not discernible in the 

 specimen referred to. The upper slender end of the scapula 

 is opposite the side of the vertebral column, about the fifth 

 neurapophysis from the head, and it curves gently downward 

 and forward, expanding at its humeral end. This expansion 

 is more sudden in the fully-developed animal, giving the bone 

 the shape of a rudder, and the direction of the scapula is 

 changed. At least in the specimens (the great majority) in 

 which the skeleton is seen from above, the slender dorsal end 

 of the scapula is seen overlying, or near the hinder border of 

 the lateral throat-plate, and it extends outward and backward 

 to its expanded humeral end. The coracoids (52) are repre- 

 sented by a pair of flat reniform plates, with the convex border 

 turned forward, the concave one backward ; they seem to have 

 overlapped the smooth margins of the posterior half of the 

 median throat-plate. It is most probable that, as in. AwjJi iuma, 

 a portion of the broad coracoid remained in the cartilaginous 

 state, and that the full reniform plate answers to the ossified 

 part of that coracoid which it resembles in shape and relative 

 position. The position of the slender scapula 1 , styliform and 

 rib-like, as in the Perennibranchiates, is instructively shown 

 in t. xviii., figs. 1 and 2, of M. von Meyer's treatise. The 

 coracoids, as in Amphvuma, form the chief pari of the articular 

 cavity for the humerus. 



The perennibranchiate affinities of A rchegosaurus are shown 

 as clearly by the scapular as by the hyoidean arch. The fore- 

 limb does not exceed half the length of the head. The humerus 



