200 



HEALTH AND DISEASE 



vessels, and is besides generally roughened for the attachment of the 

 sensitive laminae. A pointed process (coronal process] projects upward 

 from the superior border in front, which affords attachment for the tendon 

 of the extensor pedis muscle. 



The under surface is concave, and presents (1) a crescentic ridge (semi- 

 lunar crest] to which the tendon of the flexor pedis is attached; (2) behind 

 this two considerable openings (plantar foramina], through which pass 

 the plantar arteries and nerves; (3) still farther back a roughened surface, 

 to which the inferior ligament of the navicular bone is connected. The 

 upper surface is divided by a slight ridge into two shallow cavities, with 

 which the lower extremity of the coronet bone articulates. At the posterior 



border of this surface a 

 narrow, smooth, transverse 

 space is provided for the 

 articulation of the navicular 

 bone with the foot - bone. 

 Projecting backward from 

 the inferior border behind 

 are two bony processes, one 

 on either side, termed alee, 



or wings. 



Fig. 307. Os Pedis (Side View) 



A Coronal Process. B Superior Border. c, D Basilar and Re- 

 Irossal Processes, forming one of the alae or wings. E Preplantar 

 Fissure. F Facet for Insertion of the Extensor Pedis. 



Os Naviculare or 

 Shuttle Bone (fig. 305).- 



The navicular bone is a small 

 flattened bone, broad in the 

 middle and tapering towards 

 each extremity. It is situated 

 in the hoof, below the os 



coronse and behind the os pedis, with both of which it articulates to form 

 the coffin-joint. The great flexor tendon passes over its under surface, 

 and between the two a synovial membrane exists to lubricate the surfaces 

 of contact and facilitate movement. The anterior border articulates with 

 the foot-bone, as already explained, and is connected below with the 

 inferior navicular ligament. The posterior border affords attachment to 

 the posterior navicular ligament. To the pointed extremities are attached 

 lateral ligaments which unite the bone with the os pedis, the lateral car- 

 tilages, and the coronet bone. 



The navicular bone is the seat of that very common ailment, navicular 

 disease. 



