THE ANTERIOR LIMBS. 115 



Body. — Flattened before and behind, this bone exhibits : an anterior face^ 

 round from one side to the other, and slightly roughened above and below ; 

 a posterior face, flat, covered with ligamentous imprints in the form of a triangle 

 with the base reversed ; two lateral borders, thick, rounded, and provided with 

 some imprints. 



Extremities. — The superior, the largest, presents : Above, an articular surface 

 adapted to the inferior metacarpal surface, and consequently composed of two 

 glenoid cavities separated by a groove running from front to back ; laterally, 

 and a little posteriorly, a well-defined tubercle of iiisertion. The inferior extremity 

 has a transversely elongated articular surface, to articulate with the second 

 phalanx ; this surface is formed by tivo condyles separated by a middle groove, 

 and surmounted laterally by a small tuberosity for ligamentous insertions. The 

 external condyle is smaller than the internal, and when the bone is placed upon 

 a horizontal plane, the anterior face turned upwards, it only touches by three 

 points— the two tubercles of the upper extremity and the internal condyle ; by 

 pressing on the external condyle, it is easy to make the bone oscillate. 



The first phalanx is a very compact bone, and is developed from two points 

 of ossification, one of which is for the superior extremity alone. Professors 

 Yachetta and Fogliata, of Pisa, assert that this bone, as well as the second phalanx, 

 has three centres of ossification during uterine life. 



Sesamoids (Figs. 72, 7^). — These are two small, short bones placed side 

 by side behind the superior extremity of the first phalanx, the articular sur- 

 face of which it completes, as it has not extent enough to be exactly adapted to 

 the metacarpal surface. Each of these bones represents a small, irregularly shaped 

 polyhedron, or, rather, a short trifacial pyramid. It offers : an anterior face, 

 which is articular, and corresponding to the inferior extremity of the principal 

 metacarpal bone, moulded, as it were, on one of the condyles and one of the 

 sides of the median ridge ; a posterior face, covered with cartilage in the fresh 

 state, and forming, with that of the opposite bone, a gliding concave surface for 

 the flexor tendons of the phalanges ; a latercd face, studded with ligamentous 

 imprints ; a summit, directed upwards ; and a base, turned downwards, and 

 serving for the attachment of several ligaments. 



Second (or Median) Phalanx (Os Coron.^, Small Pastern Bone (Figs. 

 72, 73). — This is a short bone, situated in the same oblique direction as the 

 first phalanx, and between it and the third. Its general form is that of a 

 cube flattened before and behind, and offering the following features : an anterior 

 face, covered with some slight imprints ; a posterior face, provided, above, with a 

 transversely elongated gliding surface ; a superior face, channeled by two glenoid 

 cavities, to match the inferior articulating surface of the first phalanx ; an inferior 

 face, formed on the same plan as the last — being occupied by two unequal condyles, 

 which articulate with the third phalanx and the navicular bone ; two lateral faces 

 exhibiting a very marked imprint. In the interior of this bone is found a nucleus 

 of very condensed spongy substance, enveloped in a layer of compact tissue. 



It is usually developed from a single centre of ossification, though in many 

 subjects there is a complementary nucleus for the superior articular and the 

 posterior ghding surface. 



Third (Distal or Ungual) Phalanx, Os Pedis (Pedal or Coffin Bone) 

 (Figs. 72, 73, 74). — This is a short bone which terminates the digit, and sustains 

 the hoof that incloses it and the navicular bone. When completed by a special 

 tibro-cartilaginous apparidus, it represents the segment of a very short cone. 



