686 



PROF. T. H. HUXLEY OBSERVATION'S 



of the hone. I conclude, therefore, that the soft parts and any horny 

 sheath that may have existed must have decomposed and left the 

 bone bare before the sandy matrix set round the imbedded skeleton. 



Of the bones which enter into the composition of the shoulder- 

 girdle of Hyperodapedon, the specimen presents remains of the 

 interclavicle and the clavicle, the coracoid, and the scapula. The 

 interclavicle is a long narrow bone, thin and spatulate towards its 

 posterior end. The anterior end bends somewhat sharply towards 

 the dorsal side ; but the shape of its extremity, and whether it was 

 provided with transversely elongated lateral processes or not, cannot 

 be ascertained. On the left side it is in connexion with a strong 

 and long curved bone, which is obviously a clavicle. Nothing more 

 than the edge of a bone which I take to be the scapula can be seen, 

 but the left coracoid is well preserved. It is a cheesecutter-shaped 

 bone, with a broad blade and a comparatively narrow neck, which 

 widens out again to the glenoidal extremity. 



In Splienodon, the anterior end of the interclavicle is not bent 

 upwards, and is produced into two strong transverse arms, with which 

 the clavicles are articulated. The scapula and the coracoid very 

 early became undistinguishably united ; while, in Hyperodapedon, 

 they appear to have remained, as usual, separate. 



The principal bones of the left fore limb are seen nearly in their 

 natural relations (Plate XXVI. fig. 11). 



The humerus has a widely expanded proximal end of a rhomboi- 

 dal shape. In the middle, the shaft is rounded for a short distance 

 and then expands into the broad and thick distal end, the ventral 

 face of which presents a deep intercondyloid fossa. On the inner 

 side there are indications of a " median " canal. The ulna is stout, 

 with a prismatic olecranar prominence, and is somewhat curved longi- 

 tudinally so as to be concave to the interosseous space. The radius is 

 more slender and nearly straight. 



The structure of the carpus is not recognizable. The five meta- 

 carpals are preserved in various conditions of completeness. The 

 most remarkable feature about them is that they do not seem to 

 have differed to any notable extent in length (17 millim.) ; but while 

 the first, second, and third are proportionally very broad (about 10 

 millim.), the fourth has a width of not more than 7 millim., and 

 the fifth of 5 millim. 



The humerus, radius, and ulna in Splienodon, though more slender, 

 are very similar; but the ulna is longer in proportion to the radius ; 

 the first metacarpal is considerably shorter and at the same time 

 thicker than the second, while the second and fourth are a little 

 shorter than the third, and the fifth is about as long as the first ; 

 and all have much slenderer proportions than those of Hyperoda- 

 pedon. The fore foot of the extinct Lizard must in fact have been 

 remarkably short and thick in its proportions. 



