176 PROCEEDINGS OF THE ACADEMY OF [1894. 



great tendon running through the front part of the biceps brachialis 

 has a very short leverage below and a long one above.^ 



In the hind leg you will notice that the feraora-tihial joint is well 

 back, while the astragalo- tibial joint is well forward, and the tendon 

 in front of the tibia takes a longer leverage above than below, with 

 this condition reversed in the two tendons behind the tibia. 



When a horse stands in his usual position, the tendons which I 

 have drawn sustain his weight in stable equilibrium, because his cen- 

 tre of gravity is at the lowest point of its trajectory. 



The upper end of the dissected leg w^eighted heavily and moved 

 backward and forward in the vicinity of the standing position, will 

 there describe as a trajectory a flattish curve with its concavity up- 

 wards. At the lowest point of this concavity the leg settles when 

 the horse ceases his muscular effort and simply stands. Any mus- 

 cular effort that the horse may make from the standing position be- 

 gins by raising himself (A horse may, and often does, especially in 

 haunching himself, maintain his weight at a still higher point be- 

 hind by raising himself and slipping his patella over the inner troch- 

 lear surface of the femur, where it locks itself, and the weight of the 

 trunk is again sustained without muscular effort. To unlock the pa- 

 tella traction is made by the tensor vaginre femoris). 



To investigate the action of a muscle I believe it necessary to 

 consider it, not only with reference to the levers to which it is at- 

 tached, but with relation to the whole movement of the animal. 

 Then it will be seen that many muscles rated in the books as antago- 

 nistic, are no more so than are two parts of the same muscle. As an 

 exam])le, let us take the gastrocnemius. It is a short muscle, and 

 takes its origin above the knee, and is inserted by means of a long- 

 tendon (the tendo Achillis) into the calcaneum. It is said in standard 

 anatomies of the horse to be a flexor of the knee joint, of the leg on 

 the thigh, and also to bean extensor of the ankle joint. As a flexor 

 of the knee joint the muscle would be antagonistic to the great triceps 



^ The anatomist would express these facts as follows : 



The distal end of the scapnla and the proximal end of the humerus are not 

 all engaged in the formation of the shoulder-joint. The joint, indeed, lies well 

 back and constitutes less than one-third of the relatively enormous area. I wish 

 particularly to have noted, that the contact lietvveen the surfaces in the joint 

 takes place as shown iu figure 3, near the re-entering posteriorly placed angle, 

 which is formed between the scapula and the huiuerus, while, as opposed to this, 

 tlie contact at the elbow joint lietween the distal end of the Inimerus and the 

 in-oximal end of tlie radius takes place well forward, so as to be near the re-enter- 

 ing anteriorly i)laced angle between these two hones. H. Allen. 



