ABTICULATIONS OF TSE ANTEBIOB LIMBS. 157 



surface for the perforans tendon (Fig. 89, 5). It is confounded, laterally, 

 with the two branches of the perforatus, and receives in the middle of its 

 superior border the insertion of the inferior superficial sesamoid ligament. 



Mode of union. — Two lateral ligaments, .to which are added, behind, the 

 fibro-cartilage just described, and in front the tendon of the anterior 

 extensor of the phalanges, These ligaments are large and thick, and passing 

 obliquely downwards and backwards, are inserted, superiorly, into the 

 lateral tubercles on the inferior extremity of the first phalanx. They are 

 attached, beneath, to the sides of the second phalanx. Their most inferior 

 fibres are even prolonged below that point to reach the extremities of the 

 navicular bone, and constitute the posterior lateral ligaments of the pedal 

 articulation. 



Synovial membrane. — This covers the tendon of the anterior extensor of the 

 phalanges, the lateral ligaments, and the glenoid fibro-cartilage. Behind, it 

 forms a cul-de-sac which extends between the latter and the posterior face of 

 the first phalanx. 



Movements. This imperfect hinge is the seat of two principal movements : 

 extension and flexion. It also allows the second phalanx to pivot on the first, 

 and permits some lateral movements. 



In the Ox, Sheep, and Goat, the glenoid fibro-cartilage is confounded wifh the per- 

 foratus tendon, and ia only attached to the first phalanx by two lateral bands. The 

 internal lateral ligament cqmprises two fasciculi : one, very short, which terminates ia 

 the second phalanx ; and another, very long, descending to the internal face of the third 

 phalanx. The external is very thin, and is also prolonged to the terminal phalanx ; so 

 that the two last iuterphalangoal articidations of each digit are fixed by two common 

 lateral ligaments which correspoud exactly, by their position and inferior attachments, 

 to the anterior lateial ligaments of the peilal joint of Solipeds. 



In the Dog and Cat, the glenoid cartilage, also confounded by its posterior face 

 with the perforatus tendon, only adheres to the first phalanx by some cellular bands. 

 The two lateral ligaments pass from the inferior extremity of the first phalanx to the 

 superior extremity of the second. 



In the Fig, there is somewhat the same arrangement as in Carnivora. The external 

 lateral ligament is, nevertheless, more lilce that of the Horse, in its most anterior fasciculi 

 being prolonged to the external extremity of the navicular bone. 



8. Articulation of the Second Phalanx with the Third, Second Interphalangeal 

 Articulation, or Articulation of the Foot. 



To form this imperfect hinge-joint, the second phalanx is opposed to the 

 third, and to the navicular bone. 



Articular surfaces.— Oa the inferior face of the second phalanx there are 

 two lateral condyles and a median groove. On the superior face of the 

 third phalanx and the navicular bone, are two glenoid cavities separated by 

 an antero-posterior ridge. The two bones which form this last surface arti- 

 culate with each other by an arthrodia ; the navicular bone presents for this 

 purpose an elongated facet on its anterior border ; the os pedis also offers 

 an analogous :facet on the posterior contour of the principal articular surface. 



Mode of union. — -Five ligaments : a single interosseous one which joins 

 the navicular to the pedal bone; and four lateral pairs, distinguished as 

 anterior and posterior. 



a. Interosseous ligament. — This is formed of very short fibres which are 

 inserted, behind, into the anterior groove of the. navicular bone; and in 

 front, into the posterior border and inferior face of the third phalanx. This 

 ligament is lined, on its superior surface, by the synovial membrane, and oa 

 its inferior face is covered by the navicular sheath. 



h. Anterior lateral ligaments. — These are two thick, short, and wide 



