=Gastrocnemius= (Fig. 83, 9, 11; Fig. 84, 13, 14; Fig. 86, 7, 9; Fig. 88, 13).--The external and internal heads of the gastrocnemius, distinct from one another only in their upper portion, arise from the shaft of the femur, above the condyles, on the borders of the popliteal surface, to a relatively considerable extent in the great quadrupeds. At this level they are situated in the popliteal region--that is to say, in the space limited externally by the biceps, and internally by the semi-tendinosus. But as they descend to a rather low level on the leg in quadrupeds, and especially in carnivora, they do not, properly speaking, determine a projection of the calf of the leg. However, they pass from this region but to be soon continued by a tendon--the tendo-Achillis, which is inserted into the calcaneum. Now, the region of the tarsus is called by veterinarians _the ham_, the posterior surface of which is angular, because of the oblique direction of the leg with regard to the vertical direction of the metatarsus and the presence of the calcaneum; the prominence which this surface presents has received the name of _the point of the ham_, and the tendon which ends there that of _the cord of the ham_. But the tendo-Achillis does not alone form this cord. Indeed, as we will soon see, the tendon of the superficial flexor of the toes takes part in its formation. We may add, with regard to the tendo-Achillis, that it is more clearly perceived as an external feature, because the skin sinks in front of it, as it does in man, over the lateral parts of the region which it occupies. The gastrocnemius, when it contracts, extends the foot on the leg. It serves to maintain the tibio-tarsal angle in the standing position, and during walking, to determine the steadying of the hind-limbs, which then, after the fashion of a spring, project the body forward. By an analogous movement they take part in the posterior projection of the hind-limbs in the act of kicking; but they are not the only ones to act in this case, the muscles of the buttock and thigh also being brought into play. =Soleus= (Fig. 83, 10; Fig. 86, 8).--This muscle, much less developed in quadrupeds than in man, does not exist in the dog. With regard to the soleus in the pig, Professor Lesbre says: 'Meckel denied its existence; we, however, believe that it is united to the external head of the gastrocnemius, its origin being transferred to the femur.'[32] [32] F. X. Lesbre, 'Essai de Myologie comparée de l'homme et des mammifères domestiques en vue d'établir une nomenclature unique et rationelle,' Lyon, 1897, p. 169. But in animals in which it exists, this muscle, of but little importance, occupies the outer side of the leg. It arises above from the external tuberosity of the tibia, and terminates below in a tendon which is united with that of the gastrocnemius. The soleus has the same action as these latter.