73 



' sides ' of the wedge : the sides of the phalanx are the ' margins ' of the wedge : the 

 dorsal surface forms the base, the plantar or under surface is represented by the two 

 processes of the cleft apex or edge of the wedge. The proximal articular surface presents 

 a longitudinal channel, convex vertically, concave transversely, from which a flat surface 

 extends from nearly the whole of the tibial side, and a convex surface from the upper 

 part of the fibular side ; the whole articular surface being the counterpart of that on 

 the metatarsal (ib. m), with which the present remarkable bone is, by this interlocking 

 joint, firmly united. The lower prominence of the median rising of the distal joint of 

 the metatarsal (p) protrudes through the lower notch in the phalanx (»). A yielding, 

 elastic, slightly-sliding movement was all that could take place between these bones. 

 The complex distal articulation is adapted to an equally restricted junction with the 

 enormous terminal phalanx ( 3 ) ; it consists of four distinct articular surfaces, two on the 

 anterior and two on the upper part of the connate phalanges (1 & a). The internal of 

 the two distal surfaces is the largest and is slightly concave, the external one, near the 

 upper and outer angle of the bone, is slightly convex ; they are divided by a rough tract, 

 indicating strong ligamentous union with the claw-phalanx, of half an inch in breadth ; 

 and they cover the smaller proportion of the distal surface of the bone. Below the 

 outer articular surface there is a protuberance, with a smooth but non-synovial surface 

 in the present bone, which is adapted to a definite smooth surface upon the claw- 

 phalanx. The two upper surfaces are subcircular, each about half an inch in diameter, 

 very slightly convex, and about 5 lines apart. 



The great terminal phalanx of the present toe (Plates XXV. & XXVI. in, ») is 

 modified, like its homotype on the fore foot, for the firm fixation and development of a 

 powerful claw, the hollow base of which covered the bony core, and was encompassed 

 by a bony sheath of 5 inches in length. 



The base of the phalanx, whence both core and sheath extend forward, is a surface of 

 a long, narrow, vertically elliptical form, with the upper third produced backward so as 

 to overhang or cover the confluent supporting phalanges ; and the lower third sloping 

 forward at nearly the same angle with the vertical middle third, but terminated by a 

 backwardly projecting ridge. There are two articular surfaces on the middle division, 

 two on the upper division, and one on the lower division of the base. The innermost 

 of the middle articulations is slightly convex, the outermost as slightly concave ; they 

 both look directly backward. The lower articular surface is flat and subcircular ; it is 

 on the hinder and outer angle of the lower third of the base, and looks downward and 

 a little backward ; the two small surfaces on the upper third of the base are subcircular 

 and flat, and look downward : these different articular surfaces are counterparts of those 

 on the distal and upper parts of the connate phalanges. On each side of the lower 

 third of the base of the claw-phalanx is a large canal, leading forward to the interspace 

 between the bony core and sheath of the claw, and giving passage to the vessels and 

 nerves of the formative matrix of that instrument. The tibial side of the sheath 

 (Plate XXV. fig. 1, 3) is gently convex ; the fibular side (Plate XXVI. fig. 3, s) is flatter : 



l2 



