POSTERIOR MEMBER. 247 



limited in front by the tibial crest and behind by the tendon of the gastrocnemius 

 and perforatus muscles {cord of the hock, incorrectly called the hamstring tendon), 

 which is inserted on the summit of the calcaneus. 



The internal face, almost plane and subcutaneous, is traversed by the 

 saphena vein, which is accompanied by the artery of the same name and several 

 lymphatic vessels, voluminous but not visible in the normal state. The very lowest 

 extremity of this face displays in relief the internal tuberosity of the tibia, as 

 well as the corresponding portion of the tendo Achillis, and, between these two, 

 the concavity already indicated under the name hollow of the hock. 



Movements. — The leg, owing to its mode of articulation with the 

 thigh, is the seat of two principal movements, flexion and extension. 



During the former, the leg is carried upward and backward ; the 

 femoro-tibial angle is closed in proportion to the length of the flexor 

 muscles. Flexion commences in the latter part of the phase of con- 

 tact, and is completed a little after the raising up of the foot. It does 

 not entail much fatigue on the agents which execute it, as they have 

 only to overcome the weight of the member to be raised. 



As soon as the thigh has eff'ected its forward movement, the leg 

 rapidly completes its own, and the amplitude of the arc of a circle 

 thus described by its inferior extremity depends always (apart from the 

 length of the tibia itself) upon the degree of flexion which it effects 

 and the distance at which the foot was raised above the ground. If 

 the foot is not raised high enough at the moment when it is to come 

 down on the ground, the hoof will be in contact again before the leg 

 has had sufficient time to attain the maximum degree of extension of 

 which it is capable. Indeed, it is evident that the length of the step is 

 in direct ratio with that of the tibial extension. 



Length. — The length of the leg is measured from the inferior 

 part of the stifle to the fold of the hock. It is always equal to that 

 of the forearm, and should be as extensively developed as possible in 

 rapid motors. Upon it depends, indeed, the extent of the movements 

 undergone by its inferior extremity, at the same time that it implies a 

 proportional length of the muscles which belong to this region ; more- 

 over, as these muscles are destined to move the canon, it follows that, 

 for these two reasons, a long leg is indispensable to the velocity of the 



gait. 



If it be too short, the foot passes over less surface at each step ; the 

 animal can only preserve his speed by dint of multiplying his move- 

 ments and increasing his fatigue. It is needless to say that this con- 

 formation offers nothing objectionable in slow motors, from which 

 nothing more is expected than great muscular power. 



The length of the leg deserves, likewise, to be studied in relation 



