AND AVES OF NORTH AMERICA. 



109 



r 



External Form and Posture of Laelapx. — The short fore limbs of this genus suggest 

 at once the habit of using the hind limbs chiefly, yet this disproportion is no sufficient 

 reason therefor, and is seen to exist in the tailless Batrachia, where no such position is 

 assumed. It exists to a less degree among the modern lizards, whose position we well 

 know to be always horizontal. 



Laelaps bad, however, no doubt an ereet position for the following reason: The head 

 and neck of the femur are at right angles to the direction of motion on the condyles, or in 

 the same plane as the transverse direction of the condyles. This indicates that the femur 

 has been flexed, and extended in a plane parallel with that of the vertebral column. The 

 relations of articulation are those of birds and different from those of reptiles, where the 

 directions of the proximal and distal condyles of the femur are oblique to each other, and 

 the proximal, of vertically elongate form, thus allowing the femur to be obliquely directed 

 as regards the axis of the body, so that in a, prone position it rested on the ground 

 equally clear of the body and the "Hexed tibia.. 



The resemblance of the tibia, with its high crest and embracing astragalus, as well as 

 the slender fibula,, to those of the birds, confirms this position; so do types of the iliac 

 and sacral structures. The same is suggested by the great bird-like reptile tracks found 

 in many places. 



How must a reptilian form with, elongate vertebral column and heavy tooth-bearing 

 cranium have stood erect! The elongate form of the femur, as compared with the tibia, 

 is only seen in man, who walks erect ; in the birds and kangaroos the lemur is very much 

 shorter than the tibia,; besides these, no other vertebrates walk on the hind limbs, 

 entirely or in part. The lizards, which are prone, present the long femur exceeding or 

 equalling the tibia. 



The bird-like reptile did not, however, exhibit the slight flexure between femur and 

 tibia, presented by man. The acetabulum in the; known Dinosauria is not or but weakly 

 completed below, or what would be in man anteriorly, indicating that the weight of the 

 body was supported by a, femur placed at a strong angle with the longitudinal axis of the 

 ilium; otherwise the head of the femur would be most readily displaced. I£ therefore, 

 the ilium were more or less erect, the lemur was directed forwards; if horizontal, the 

 femur must have projected downwards. I have shown, however, that the position and 

 therefore! the ilium was oblique or erect; therefore the lemur was directed very much 

 forwards.* 



* The remarks of Prof. Owon on tins relation in Megalosaurus arc so pertinent, that they are introduced here : 

 " The hack ward position and production of the corresponding articular prominences or condyles in both femur 

 and tibia indicate that these hones were joined together at an angle, probably a, right one when in their intermediate 



state, between flexion and extension ; and that the motion of the tibia, could not have taken place to the extent 

 required to bring the two bones to the same line." 

 AMERI. PHILOSO. SOO. — VOn. XIV. 28 



