368 THE MUSCLES. 



fleshy fasciculi distinct from one another only at their superior extremity, being 

 confounded for the remainder of their extent, and continued inferiorly by a 

 single tendon which extends to the point of the os calcis. 



Form — Stnicture. — Both of these muscular masses are flattened on both 

 sides, thick in the middle, narrow at the extremities, and intersected by strong 

 tendinous bands. By their union they form a wide channel, open in front, which 

 embraces the femoro-tibial articulation and the muscles of the deep layer. 



The tendon, at first fasciculated, then single and funicular, receives that of 

 the soleus, and is reinforced by a fasciculus from the fibrous band annexed in 

 front to the tendon of the perforatus (see the description of the tibial aponeurosis, 

 p. 362). An aponeurotic layer which covers the gastrocnemius, is continued 

 downwards, partly with the fibrous band, and partly with the tendon of the 

 muscle itself. 



Attachments. — The external gemellus arises on the femur, from the rugged 

 lip which margins the supra-condyloid fossa in front ; the internal, from the 

 collection of tubercles which constitutes the crest of the same name. The 

 terminal tendon of the two bellies is fixed on the summit of the os calcis, not at 

 its anterior part, but posteriorly ; this being lubricated by a bursa that forms a 

 gliding surface on which the tendon rests during extreme flexion of the foot 

 (Fig. 101, 1). 



Relations. — By their superficial face, to the three ischio-tibial muscles, and 

 the tibial aponeurosis ; by their deep face, to the perforatus — which adheres 

 intimately to the vastus externus — to the posterior ligament of the femoro- 

 tibial articulation, the popliteal muscle and vessels, the great sciatic nerve, and 

 the oblique and deep flexor muscles of the phalanges. The tendon lies beside 

 that of the perforatus, which is twisted around and completely envelops it at 

 its inferior extremity, in common with the fibrous band from the tibial aponeu- 

 rosis. The two tendons form what is usually termed the tendon of the hock, or 

 tendo Achilles. 



Action. — The gastrocnemius extends the foot upon the tibia. It acts as a 

 lever of the first order when the limb is raised from the ground, and as one of 

 the second order when the hoof is placed on the ground. It maintains the 

 tibio-tarsal angle while the animal is standing, and in progression gives to the 

 hock that spring which carries the body forward. 



2. Soleus (Plantaeis) (Fig. 201, 21). 



Synonyms. — Bourgelat and liis successors have erroneously assimilated it to the plantaris of 

 Man. In regarding this little muscle as the soleus, we conform to the well-founded opinion 

 of Cuvier. It is the peroneo-calcaneus of Girard. 



Form — Situation. — This is a thin, long, and riband-shaped rudimentary 

 muscle, situated at the external side of the leg, between the tibial aponeurosis 

 and the muscular portion of the perforans. 



Attachments. — It is fixed, by its superior extremity, behind the supero-external 

 tuberosity of the tibia ; and terminates, inferiorly, by a small tendon, which joina 

 that of the gastrocnemius. 



Action. — It is a feeble auxihary of the last-named muscle. 



