WEALUEN DINOSAURS. 377 



The fourth metapodial (Pis. 43 and 44, iv), which is here the third fully deve- 

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

 end 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 (PI, 44, 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 (PI. 43 and 44, n i, 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 i) is 4^ inches in length; its proximal surface is obliquely 

 sub-quadrate, very slightly concave, with the upper and outer (fil)ular) 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 

 expanding as it descends; concave, but in a less degree, transversely; with the inner 

 (tibial) side of greater extent. On both sides the articular border is slightly raised, 

 forming the lower boundary of the wide concavity for the attachment of the lateral 

 ligaments. 



The second phalanx (n 2) is broader than it is long, its extreme breadth 

 being 2 inches 4 lines. The proximal articular surface, with its concavity and con- 

 vexity the reverse of those of the surface on which it plays, is triangular, with the 

 angles largely rounded off. The under surface of this phalanx is somewhat flattened ; 

 the upper surface is contracted ; the distal trochlea, very convex vertically, is flat 

 transversely, at its upper half, slightly concave below ; the modification resembling 

 that of the phalanx supporting the unequal one in the other toes. 



The third phalanx (n 3), which supported the claw, presents an oblique basal 

 articular surface, flattened transversely and produced backwards above; slightly 

 convex transversely below. The unequal part is sub-depressed, obtuse, obliquely 

 bent downwards and outwards, but in a slight degree ; the base of the bone is notched 

 at each side, where the vascular canals relating to the growth of the claw commence ; 

 they impress the upper and lateral parts of the bone, which is 4J inches in length. 



The proximal phalanx of the middle toe (PI. 43 and 44, m 1), answering to the 



