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also convex from above downwards. The proximal surface is continued upon 

 the two inferior tuberous angles of the phalanx, to form the sesamoid articula- 

 tions : the bone slightly contracts transversely to the upper part. The middle 

 phalanx is longer in proportion to its breadth, which is greatest in the vertical 

 diameter of its base, both upper and lower ends of which are produced in the 

 form of tuberosities beyond the trochlear articulation, hmiting the extent of 

 vertical movement, and giving attachment to the tendons. Anterior to these 

 tuberosities are cavities, one on the upper, the other on the lower surface of the 

 bone ; the upper one being the deepest, and receiving the projecting part of the 

 proximal end of the last phalanx. The sides of the middle phalanx are nearly 

 flat : the proximal articulation is concave vertically, and traversed by a median 

 obtuse ridge : the distal articulation describes a semicircle, and is excavated by 

 a deep median groove. In this groove the corresponding ridge on the articular 

 surface of the distal phalanx plays, while the deep lateral concavities of that 

 surface receive the semicircular convexities of the preceding joint : a very pow- 

 erful ginglymus, restricted to vertical movements, is thus produced, while the 

 backward production of the upper part of the joint permits the claw-bone to be 

 bent only downwards. The broad, rough, quadrilateral base of the claw-sheath 

 presents the two usual perforations ; and from the sides of this base the bony 

 sheath arches over the basal half of the supporting process. This is conical, 

 nearly straight, with an obhque base which gives the under only half the length 

 of the upper part ; the upper part presenting a regular convexity from side to 

 side, flattened towards the apex, and divided by two sharp edges from the less 

 convex under surface. The transverse and vertical diameters of this phalanx 

 are equal. 



The three phalanges of the middle digit very closely resemble those of the 

 preceding except in size, which exceeds that of the second as much as this does 

 the first digit. The proximal phalanx is characterized by the greater protube- 

 rance of its outer and inner sides, and the proportionally larger surfaces for the 

 sesamoid bones. The middle phalanx is rather shorter in proportion to its 

 breadth and depth than in the second digit. The ungual phalanx has double the 

 dimensions of that of the second digit : the basal, or inferior plate, is flatter, but 

 is raised into one protuberance. The claw-process is more curved, and its sides 

 converge more to the upper surface, which is, however, convex, except near the 



