THE FIRST PHALANX 



101 



consisting of two glenoid cavities separated by a sagittal groove; the medial cavity 

 IS a little larger than the lateral one. On each side is a buttress-like tuberosity for 

 ligamentous attachment. The dorsal surface has a slight elevation for the attach- 

 ment of the extensor tendons. 



The distal extremity (Extreraitas distalis) is smaller, especially in its dorso- 

 volar diameter. It presents a trochlea for articulation with the second phalanx, 

 consisting of a shallow sagittal groove separating two condyles; the medial con- 



Intermediate groove 



Proximal articular surface 



Tuberosity 



Emiiicucv for extensor tendons 



First phalanx 



Dorsal surface -- 



Eminence for collateral liganicut - 

 Distal articular surface -- 



Proximal articular surface ■- 



Dorsal surface - 



Eminence for collateral ligament - 



Distal articular surface - 



Articular surfi 

 Angle _ 



Depression for collateral 



ligament ~ J 



Dorsal groove - 

 Coronary border - 

 Articular surface - 



Extensor process 



Dorsal surface 



Distal border :'-;C f < 



Fig. 79. — Phalanges and Distal Sesamoid of Horse; Dorsal Aspect. 



Second phalanx 



Third sesamoid 



Third phalanx 



dyle is a little the larger, and the two are separated posteriorly by a notch. On 

 either side, just above the margin of the articular surface, is a depression sur- 

 mounted by a tubercle, to both of which the collateral ligament is attached. Be- 

 hind the tubercle is a distinct mark to which the superficial flexor tendon is 

 attached. 



Development. — The first phalanx ossifies from three centers. The distal end 

 unites with the shaft before birth, the proximal end at about one year of age. 



The first phalanx contains a small medullary cavity in the middle of the shaft. It may be 



