158 TEE ABTICULATI0N8. 



fasciculi, attached by their superior extremities to the lateral imprints of the 

 second phalanx, and by their inferior extremities into the two cavities at the 

 base of the pyramidal eminence of the os pedis. Each ligament is partly 

 covered by the complementary fibro-cartilage of that bone, and appears to 

 form a portion of it. Its anterior border is continuous with the common 

 extensor tendon of the phalanges; its internal face is covered by the 

 synovial membrane, which adheres closely to it. 



c. Posterior lateral ligaments. — These have been already noticed. 

 Each is composed of the lowermost fibres of the lateral ligament of the first 

 interphalangeal articulation ; these fibres, after being attached to the 

 second phalanx, unite into a sensibly elastic fibrous cord, which is chiefly 

 fixed into the extremity and superior border of the navicular bone, where the 

 ligaments join each other, and in this way form a kind of complementary 

 cushion which increases the navicular articular surface. It also sends off 

 a short fasciculus to the retrossal process, and a small band to the internal 

 face of the lateral fibro-cartilage. Partly concealed by the latter and the 

 plantar cushion, this ligament is covered inwardly by the articular 

 synovial membrane. 



(For full details as to the manner in which the navicular is attached to 

 the pedal bone, the student is referred to the series of papers on the Horse's 

 Foot, published by me in the ' Veterinarian ' for 1870. It is only necessary 

 to refer here to the intimate connection there exists .between the lateral and 

 interosseous ligaments, and the stratiform fibro-cartilage covering the pos- 

 terior face of this sesamoid : a connection, or rather unification, which has 

 been strangely overlooked by hippotomists and hippo-pathologists, but 

 ■which has undoubtedly a most important bearing on the genesis of that 

 very prevalent and fonnidable malady of the anterior foot of the Horse 

 — navicularthritis.) 



Synovial membrane. — This descends below the facets which unite the 

 navicular to the pedal bone. It offers, posteriorly, a vast cul-de-sac which 

 reaches the posterior face of the second phalanx, and lies against the two 

 navicular sheaths. It also forms another much smaller, by being prolonged 

 between the two lateral ligaments of the same side. This is very often dis' 

 tended, and it is liable to be opened in the operation for diseased cartilages. 



Movements. — The same as those of the first interphalangeal articulation. 



In the Sheep are found : 1, An interoBseous ligament to unite the navicular bone to 

 the third phalanx ; 2, Two anterior lateral ligaments commencing, as already stated, at 

 the first phalanx ; 3, Two lateral posterior ligaments, passing to the posterior face of the 

 second phalanx and the navicular bone (the internal is yellow and elastic) ; 4, A single, 

 .anterior, elastic ligament, attached above to the superior extremity of the second 

 phalanx, and fixed below into the third, between the insertion of the common extensor 

 of the digits and that of the internal anterior lateral ligament ; an inferior interdigital 

 ligament, situated between the ungueal phalanges, whose separation from each other it 

 limits. This ligament is composed of parallel fibres, which extend transversely from the 

 one navicular bone to the other, and is covered on its inferior face Ijy the skin of the 

 interdigital space. Its upper face is in contact with an adipose cushion. 



In the Ox, the external anterior lateral ligament, wide and expanding, is almost 

 entirely covered by the long branch of the proper extensor of the digit, to which it is 

 intimately adherent. The interdigital ligament has a much more complicated character 

 than that of the Sheep. It is formed of fibres intercrossed on the median line, and 

 divided at its extremities into two fasciculi : a superior passes over the perforans tendon, 

 to which it serves as a restraining band, and is fixed to the outside of the inferior 

 extremity of the first plialanx. after contracting very close adhesions with a strong fibrous 

 web which descends from the posterior metacarpal region, and which will be more fully 

 noticed when describing the muscles ; an inferior, shorter than the preceding, attached 

 to the internal extremity of the navicular bone and the internal face of the third phalanx, 



