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450. The large ungual phalanx of the same toe. 



The position of the trochlear cavity, which extends obliquely from 

 above downwards and forwards over the base of the ungual phalanx, and 

 the backward production of the upper end of the median trochlear ridge, 

 causes this phalanx, in extreme extension, to have its long axis parallel 

 with that of the middle phalanx : in extreme flexion the point of the 

 claw is bent down at right angles to the middle phalanx. The lateral 

 concavities receiving the trochlear convexities of the adjoining phalanx, 

 and the median ridge fitting the median canal of the same, are so deep 

 as to prevent any lateral motion, and give great strength to the joint. 

 The upper production of the basal articulation of the ungual phalanx 

 is flattened vertically, and rough ; serving probably for the implantation 

 of the extensor tendon. The osseous sheath of the claw is continued 

 forwards from the upper margin of this surface ; from the sides of the 

 articular cavity, and of the flat rough oval surface at the proximal half of 

 the base of the claw. The sheath, which varies from half a line to one 

 line and a half in thickness, appears to have extended forwards over at 

 least the basal third of the bony process supporting the claw : but it is 

 broken away more or less in both the feet. The claw process, which 

 forms the chief part of the ungual phalanx, is conical, slightly deflected, 

 and inclined inwards ; convex above and at the sides, which are divided 

 from the under surface by a sharp edge : the under surface, owing to the 

 oblique line from which the sides of the ungual sheath arise, is less than 

 half the length of the upper surface : it is convex transversely along its 

 middle part, concave on each side ; these lateral channels bounded ex- 

 ternally by the ridges above mentioned, and deepening as they approach 

 the base of the phalanx. The vessels and nerves which supplied the 

 secreting organ of the enormous claw were lodged in the above channels : 

 of the two large oval perforations in the lower rough tract, the external 

 one leads directly to the beginning of the corresponding channel, the in- 

 ternal one conducts to the cancellous structure of the phalanx. For the 

 extent of one inch and a half from the apex of the claw, the upper sur- 

 face is impressed with a shallow longitudinal channel. 



