304: THE MUSCLES. 



one of the second order when the hoof is placed on the ground. They 

 maintain the tibio-tarsal angle while the animal is standing, and in pro- 

 gression give to the hock that spring which carries the body forward. 



2. Soleus (or Solearis). (Fig. 135, 21.) 



Synonyms. Bourgelat and his 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. (Plantaris 

 Percivall.) 



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

 muscle, situated at the external side of the leg, between the tibial aponeu- 

 rosis 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, inferior ly, by a small tendon, 

 which joins that of the gastrocnemii. 



Action. It is a feeble auxiliary of the last-named muscles. 



3. Superficial Flexor of the Phalanges, or Perforatus. (Figs. 135, 25 ; 137, 30.) 



Synonyms. Femoro-phalangeus Girard. It is represented in Man by the plantaris 

 and flexor brevis digitorum, or perforatus. These two, in the majority of mammalia, 

 are united from end to end to form a single muscle. (The ga&trocnemius internus of 

 Percivall.'j 



Form Structure. The perforatus of the posterior limb is only repre- 

 sented, in reality, by a long tendinous cord, that is somewhat muscular, 

 slightly thickened, and fusiform in its upper fifth, which forms the body 

 of the muscle. 



Origin Direction and delations Termination. It originates, by its 

 upper extremity, in the supercondyloid fossa, descends between the two 

 portions of the gastrocnemii, to the external of which it is intimately related, 

 on the posterior face of the femoro-tibial articulation and the three posterior 

 deep tibial muscles. On reaching the inferior extremities of the muscular 

 bellies of the gastrocnemii, it becomes exclusively tendinous, and is directly 

 united to the fibrous band which reinforces the tendon of the hock. It 

 afterwards disengages itself below the gastrocnemius, and is placed at the 

 internal side of its tendon, then on its posterior surface, and in this position 

 gains the summit of the os calcis. There it becomes widened to form 

 a fibrous cap, which is covered by a large vesicular synovial membrane ; 

 it is moulded to the posterior region of this bony eminence, which it com- 

 pletely envelops in order to be fixed on its lateral portions, and is united 

 to the calpanean band from the tibial aponeurosis. From this point the 

 tendon of the perforatus is prolonged behind that of the perforans to 

 the posterior face of the second phalanx, where it terminates in exactly the 

 same manner as the analogous muscle of the anterior limb. 



Action. It flexes the second phalanx on the first, and this on the meta- 

 carpus. It also concurs in the extension of the foot. Its principal office, 

 however, is that of a mechanical stay, destined to sustain the equilibrium of 

 the body while the animal is in a standing posture, by preventing the 

 diminution of the angle of the hock and that of the fetlock, the femur being 

 fixed by the contraction of the crural triceps and the gluteal muscles. 



4. Popliteus. (Fig. 137, 21.) 



Synonyms. The abductor tibialis of Bourgelat, and femoro-tibialis obliquus of 

 Girard. 



