18 FOSSIL REPTILIA OF THE 



border (/), which shows a broad and shallow articular depression for the distal end 

 of the fibula. The distal articular surface for the tarsus presents the same form of an 

 oblique, wide, and shallow notch (<? ), as in the Megalosaurus. 



The largest diameter of this end of the bone is 7 inches ; the circumference of the 

 middle of the shaft is 7 inches. At the back part of the shaft, five inches from the 

 proximal end, is the orifice of a canal for the medullary artery, which passes obliquely 

 downwards. The entire length of the bone is 1 6 inches. 



Metajpodium of the Hylaosaurus. T. XI. 



The specimen, No. 2556, in the British Museum, figured in T. XI, exhibits three 

 metacarpal or metatarsal bones of the same foot, cemented, as naturally connected, by 

 the Wealden matrix. The shape of the outer ( iv) and inner ( n ) of these bones indi- 

 cates that three alone constituted their segment of the foot, unless some styliform 

 rudiment may have existed, which has left no mark of junction with the next fully 

 developed metapodial* bone. 



Those bones of the foot of the Iguanodon, described in a former part of the present 

 Monograph, and figured in T. I, II, and III, afford a means of comparison with the 

 present specimen, and show that it cannot belong to the corresponding foot of the 

 Iguanodon, and that it is very improbable that it can belong to another (fore or hind) 

 foot of the same species. It plainly indicates a foot of longer and more slender 

 proportions, with a different configuration of the metapodial bones. The relative 

 lengths of these bones show that they belong to a foot of the same side of the body 

 as that of the Iguanodon above described. 



The proximal ends of the three bones have been broken off obliquely, the outer- 

 most (T. XI, n) retaining the greatest proportion of the shaft : the innermost (ib., iv) 

 retains its distal articular surface ; the middle bone (ib., in) has a portion of the same 

 surface. The distal end of the outermost bone is broken away. 



By the analogy of the metapodium of the Iguanodon, the innermost metapodial 

 of the present specimen answers to the second in the pentadactyle foot, the middle to 

 the third, and the outermost to the fourth. The foot to which they belonged was 

 functionally tridactyle, through the arrest of development or suppression of the first 

 and fifth toes in the pentadactyle foot. 



The metapodial ( n) has a sub-compressed shaft, convex on the inner or free side 

 (figs. 1 and 2), slightly concave towards the middle metapodial ; with the anterior 



* The term "metapodium" signifies the same segment in both fore- and hind-feet, and is requisite in 

 treating of such segment when it cannot be determined whether it is of the fore-foot, metacarpus, or of the 

 hind- foot, metatarsus. 



