THE CENTRAL TARSAL BONE 



121 



It consists of a body and a medial process, the sustentacu- 



extend the hock joint, 

 lum tah. 



The body (Corpus) is enlarged at its proximal end to form the tuber calcis or 

 "pomt of the hock"; the posterior part of this eminence gives attachment to the 

 tendon of the gastrocnemius, while in front and on each side it furnishes insertion 

 to tendons of the superficial digital flexor, biceps, and semitendinosus muscles. 

 The distal extremity bears a concave facet for articulation with the fourth tarsal 

 bone. The medial surface of the body has on its lower part a strong process, the 

 sustentaculum tali, which projects inward. The process has a large, oval, slightly 

 concave facet in front for articulation with the tibial tarsal, and sometimes a small 

 articular surface below for the central bone. Its plantar surface forms with the 

 smooth medial surface of the body a groove for the deep flexor tendon (Sulcus tarsi). 

 Its medial surface has a prominence on the distal part for the attachment of the 

 medial ligament. The lateral surface of the body is flattened, except below, where 



there is a rough prominence for the attachment of the lateral 

 ligament. The dorsal border is concave in its length, smooth 

 and rounded in its upper part. About its middle is a blunt- 

 pointed projection (Processus cochlearis) which bears facets 

 on its medial and lower surfaces for articulation with the 

 tibial tarsal bone, and is roughened laterally for ligamen- 

 tous attachment. Below this are two facets for the tibial 

 tarsal, and an extensive rough fossa which concurs in 

 the formation of the sinus tarsi. The plantar border is 

 straight and broad, and widens a little at each end; it is 

 rough, and gives attachment to the long plantar ligament. 



Tuber 

 calcis 



Fig. 107. — Right Fibular 

 Tarsal Bone of Horse; 

 Dorsal View. 



1-4, Facets for articulation with 

 tibial tarsal bone ; 5, 



Fig. 108. — Right Central Tarsal Bone of Horse; Proximal Surface. 

 1, Articular surface for tibial tarsal; 2, facet for fibular tarsal; 3, non-articular 



depression. 



The Central Tarsal Bone 



The central tarsal bone (Os tarsi centrale)' is irregularly quadrilateral, and is 

 situated between the tibial tarsal and the third tarsal. It is flattened from above 

 downward, and may be described as having two surfaces and four borders. The 

 proximal surface is concave from before backward, and almost all of it articulates 

 with the tibial tarsal; a non-articular depression cuts into its lateral part, and 

 sometimes there is a facet for the fibular tarsal bone on the posterior angle. The 

 distal surface is convex, and is crossed by a non-articular groove, which separates 

 facets for articulation with the third and the first and second (fused) tarsals. The 

 dorsal border and the medial border are continuous, convex, and rough. The 

 plantar border bears two prominences, separated by a notch. The lateral border 

 is oblique, and bears anterior and posterior facets for articulation with the fourth 

 tarsal, between which it is excavated and rough. 



^ Also termed the scaphoid or navicular bone. 



