Labyrinthodon /rom Warwickshire. 539 



strong as the fore. Of the bones of these extremities there may be recognised 

 a humerus, a femur, and the two tibiae. The humerus (fig. 1, h.) is one inch in 

 length, regularly convex at the proximal extremity, expanded both at this and 

 the distal extremities, and contracted in the middle. There is a portion of a some- 

 what shorter and flatter bone, bent at a subacute angle with the distal extremity of 

 the humerus, and which presents the nearest resemblance to the anchylosed radius 

 and ulna of the Frog. Both the extremities are wanting in the femur (fig. ] , /.), 

 the shaft of which is slightly bent, and is subtrihedral ; its walls are thin and com- 

 pact, and include a large medullary cavity. The tibia (fig. 1, t.) is as long, but 

 thicker and stronger than the femur ; both tibise have lost their articular extremi- 

 ties, but both exhibit that remarkable compression of their distal portion which 

 characterizes the corresponding bone in the anourous Batrachia, and both likewise 

 exhibit the longitudinal impression along the middle of the flattened surface ; the 

 length of the most perfect of these shafts of the tibia is two inches one line. 



Associated with these bones is the extremity of a broad and compressed bone, 

 which bears most resemblance to a portion of lower jaw, but does not afford the re- 

 quisite characters for precise determination. The breadth of the entire end is one 

 inch three lines ; this is terminated by a gently convex outline ; the fragment slightly 

 contracts towards its broken end, which is one inch broad ; one surface of the frag- 

 ment is slightly convex ; the opposite surface rises into a broad, obtuse, longi- 

 tudinal ridge ; the fractured surface exhibits a central medullary cavity, sur- 

 rounded by a close cancellous structure, varying from one to tw^o lines in thickness. 

 If, as appears at first sight, it formed any part of the lower jaw, the proportions 

 of the head of this Batrachian reptile must have been enormous ; and the same 

 disproportion opposes itself to the comparison of this bone with the expanded sa- 

 crum of the Toad, or with the scapula, coracoid, ischium or pubis, at least, if we take 

 these bones in any known reptile as the standard of comparison. Nevertheless the 

 deviations from ordinary proportions which extinct species occasionally present in 

 parts of their skeleton, as e. g. the cervical vertebrae in the Plesiosaurus, the fingers 

 of the Pterodactyle, &c., forbid the rejection of the idea, that the bone in question 

 may have actually formed part of the same skeleton with the contiguous bones 

 of the extremities and vertebrae. 



The most perfect of these vertebrae is four lines in length ; the vertical diameter 

 of the articular extremity two lines, its transverse diameter one line and a half. 

 Each terminal articular surface is pretty deeply and regularly concave, with the 

 periphery convex : in two of the vertebrae these surfaces slope in a parallel direc- 

 tion obliquely from the axis of the body, as in the dorsal vertebrae of the Frog, and 

 are not, as usual in Saurians, at right angles with that axis ; so that they indicate 

 an habitual inflection of the portion of the spine formed by them, analogous to that 



