POSTERIOR MEMBER. 299 



the hoof, besides disseminating it in part upon the environing reten- 

 tive apparatus. 



The first phalanx is united behind to the sesamoid bones ; above, to the 

 principal bone of the canon through the medium of ligaments which we have 

 already enumerated. (See Fetlock.) Interiorly, it is firmly articulated with the 

 second phalanx by the lateral ligaments, e, c (Fig. 96), which are common also 

 to the articulation of the foot. 



These means of union are completed, anteriorly, by the tendon of the ante- 

 rior extensor of the phalanges ; posteriorly, by the cord of the flexors, separated 

 from the inferior sesamoid ligaments, b, b, b (Fig. 97), by the inferior cul-de-sac 

 of the great sesamoid sheath. 



Movements. — The pastern is the seat of two movements, flexion 

 and extension. Each of these modifies the opening of the metacarpo- 

 or metatarso-phalangeal angle, which, in a state of repose, can be con- 

 sidered as in an attitude of extreme extension. They have, however, 

 not the same value. Almost insurmountable anatomical obstacles, as 

 we have seen, hinder a greater extension ; these reside in the presence 

 of the suspensory ligament and the flexor tendons upon the summit of 

 this angle ; a fortunate disposition, in virtue of which the bones main- 

 tain their function in sustaining the body, without being exposed to too 

 violent eifects from the tractions of the extensive displacements of the 

 latter. The flexion of the pastern, on the contrary, has, so to speak, 

 no definite limits. The articular movement is capable not only of 

 causing a disappearance of the primitive angle, but even of giving it 

 a disposition inverse to that which it occupied at first. In this case, 

 the obstacle to the closing of the new angle is entirely mechanical ; it 

 is due to the presence of the sesamoid bones and the soft tissues, which 

 interpose their thickness between the canon and the phalangal segment. 



At the moment of the contact, when the body-weight is thrown 

 on the member, the fetlock is pushed backward and downward, and 

 the pastern tends to become horizontal. It then gradually becomes 

 straightened upon the canon until towards the termination of this 

 phase. The two segments are now almost in a straight line. The 

 pastern then becomes strongly flexed, elevates the foot, and is finally 

 placed in prolongation with the canon to commence again the phase 

 of contact with the ground. These diverse attitudes have been accu- 

 rately recorded by MM. Marey and Pages by means of instantaneous 

 photographs.^ 



Form. — The anterior face of the pastern is slightly constricted in 

 its middle, particularly in horses in which this region is somewhat 



1 Marey et Pages, Analyse cin^matique des allures du cheval, in Comptes-Rendus des 

 stances de TAcad^mie des sciences, Paris, 27 Septembre, 1866. 



