THE FIRST PHALANX 67 



THE FIRST PHALANX 



This bone is frequently referred to as the os sufFraginis, and com- 

 monly also as the long pastern bone. 



It extends obliquely downwards and forwards from the fetlock joint 

 above to the pastern joint below. 



It belongs to the class of long bones, and possesses a diaphysis and 

 two epiphyses. 



The anterior surface of the shaft is smooth and shghtly convex in 

 the transverse direction. 



The posterior surface is almost flat. It presents a V-shaped, 

 roughened area which gives attachment to the vertical and two oblique 

 strands of the middle division of the inferior sesamoidean ligament. 

 Near its upper extremity this surface also presents a roughened area on 

 either side. These areas are for the attachment of the crossed bands 

 of the deep division of the inferior sesamoidean ligament. 



The lateral surfaces are convex in the transverse direction and concave 

 longitudinally. They blend with the anterior surface. Each presents 

 about midway down the shaft a transverse groove for the accommoda- 

 tion of the perpendicular artery of the pastern. Near its upper extremity 

 each of these surfaces presents a " buttress-like " tubercle, which is 

 roughened for the attachment of the lateral ligament of the fetlock and 

 the lateral sesamoidean ligament. At its inferior extremity the lateral 

 surface presents a shallow depression, above which is a tubercle. From 

 the tubercle a ridge extends upwards and terminates about midway up 

 the shaft of the bone. The depression, tubercle, and ridge are roughened 

 for the attachment of the lateral ligament of the pastern joint. 



The superior surface of the bone is articular and is moulded on 

 to the inferior surface of the large metacarpal. Consequently it 

 presents two shallow depressions separated by a deep antero-posterior 

 groove. 



