WEALDEN FORMATIONS. 5 



and a half higher than that of the adjoining (third) metapodial, and the proximal end is 

 one inch and a half higher than that of the adjoining bone ; but this is probably due 

 to some dislocation of the metapodial before the matrix hardened around it. 



The third metapodial (ib., m) is 11^ inches in length. The proximal articular 

 surface is slightly convex ; a small portion of its back part (T. II, a) is continued upon 

 the thick process ( b ) from the back part of the bone, which rises some way above the 

 level of the horizontal surface, apparently about an inch ; but the summit of this pro- 

 cess has been broken off. This process subsides as it descends to the inner border of 

 the shaft, about halfway down. 



The inner and anterior angle of the proximal end is produced toward the second 

 metapodial, rendering the side next that bone rather hollowed out, as for its reception 

 when in its proper position. There is no process from the middle of the shaft near its 

 fore part, as in the second metapodial. The distal end (T. II, fig. 3, in) expands into 

 a broad trochlear surface, convex from before backwards, concave transversely ; the 

 fore-and-aft extent of the tibial side of this joint is the greatest ; it appears to have 

 been covered by articular cartilage, the extent of the cartilage being well defined by 

 the transverse line at which the smooth surface rises a little above the level of the 

 rough surface for ligamentous attachment. 



The fourth metapodial (T. I, II, III, iv), which is here the third fully developed, 

 and at the same time the outermost one, is 9 inches in length. Its proximal end 

 (T. II, fig. l,iv) is of a semi-elliptical form, concave towards the middle metatarsal, to 

 which it articulates in the present specimen two inches below the proximal end of that 

 bone ; but there may have been some displacement of the bone prior to fossilization. 

 The inner and posterior angle of the upper part of the shaft of the fourth metatarsal is 

 slightly produced, as is also the same angle of the shaft below its middle. The front 

 surface of the shaft is smooth and convex ; the back part is almost flat, and is crossed 

 obliquely near its lower end by a rough ridge. 



The distal articular surface (ib., fig. 3, iv) is oblique, but in the opposite direction to 

 that of the second metapodial ( n) ; the transverse concavity of the surface is slight, and 

 is also limited to the hinder half; the anterior fibular angle is produced. The extent 

 of the articular cartilage of the joint is indicated by the raised line, as in the middle 

 metapodial ; the concavity on the inner side of the distal end is deep and well defined. 



The innermost of the three toes (T. I and III, n l, 2, 3), answering to the second in 

 the hind-foot of the Iguana, includes three phalanges, and measures in total length 

 10 inches. 



The first phalanx ( n l) is 4^ inches in length ; its proximal surface is obliquely 

 sub-quadrate, very slightly concave, with the upper and outer (fibular) angle most 

 produced, but rounded off; it is notched at the middle of the lower (plantar) border. 

 Near this border, on the plantar aspect of the shaft, are two tuberosities for insertion 

 of tendons. The distal articular surface is a trochlear one, convex vertically, and 



