WEALDEN FORMATIONS. 47 



All ungual phalanges of Saurian reptiles are marked on each side by a large, 

 more or less deep and smooth groove, curved with the convexity towards the upper 

 side of the claw. These grooves convey the blood-vessels and nerves to the matrix of 

 the claw, and, in some species, sink at their distal end into the substance of the 

 claw-bone. 



But, it may be said, the bony basis or core of a frontal horn likewise supports a 

 corneous sheath, and is invested by the vascular cutis which secretes that sheath. 

 Since, however, the corneous sheath of a horn, and especially of so small a one as 

 that which arms the head of the Iguana cornuta, and, as has been imagined, also of the 

 Iguanodon, is less constantly and rapidly abraded than a claw, so the indications of 

 the vascularity and activity of the reproductive organ are much more feebly marked 

 upon the horn-core than upon the phalanx. They are also marked in a different 

 manner. The horn-core is incased by its horny sheath, its base alone being free 

 from that covering. The renovation of the horn takes place, as is well known, chiefly 

 at the base, and the numerous vascular impressions are - distributed pretty equally 

 round the base of the core. 



In the Saurian claw-bone the upper surface and sides are invested by the claw, 

 and the renovation of the corneous matter is required near the sides of the distal half 

 of the osseous cone. Hence in the phalanges of the large Saurian we see the large 

 vascular curved groove extending along each side, and the canals by which the vessels 

 and nerves emerged from the bone upon its immediately investing vascular organ of 

 the claw are most conspicuous on each side near the apex. 



Now the fossil in question exhibits conspicuously the two lateral, curved, wide and 

 deep vascular grooves, c , c', d, d', figs. 1 and 2, and each groove sinks at its distal end, 

 c/ d', into the substance of the bone ; the large oblique foramina, e, by which the 

 blood-vessels and nerves emerged to supply the secreting organ of the claw are 

 also present in greatest number on each side of the apex of the bone : these characters 

 I hold to be decisive of the phalangeal nature of the so-called horn. 



The groove on the right side of the phalanx, (figT 2, c ) as seen in a view of its 

 upper surface, which is determined by the convexity of the vascular grooves, is entire : 

 it begins about two thirds of an inch from the base, is shallow at first, but gradually 

 becomes deeper, until it sinks into the substance of the bone, (at c') .: it presents the 

 usual gentle and regular curve, convex upwards ; its length, following the curve, is 

 1^ inch; it sinks into the osseous substance nearly two inches from the broken 

 apex of the phalanx ; its breadth is between 2 and 3 lines. 



On the left side, fig. 1, a portion of the vascular groove, d, d', is obliterated by the 

 loss of part of the compact outer layer of the upper surface of the phalanx, forming the 

 median edge of the groove, but the lateral or outer, and the terminal half inch of the 

 groove where it sinks into the substance of the bone, as at d', figs. 1 and 2, is entire : 

 enough remains, therefore, to show that the groove on the left side of the phalanx had 



