MUSCLES OF THE POSTERIOR LIMBS. 369 



3. SuPEEFiciAL Flexor of the Phalanges (Flexor Perforatus, 

 Gastrocnemius Internus) (Figs. 201, 25 ; 203, 30). 



fi'j/no/ij/ms.— Femoro-phalangeus — Girard. It is represented in Man by the plautaris and 

 flexor brevis digitorum, or perforatus. Tliese two, in the majority of Mammalia, are united 

 from end to end to form a single muscle. 



Form — -Structure. — The perforatus of the posterior limb is only represented, 

 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 Relations — Termination. — It originates, by its upper 

 extremity, in the supra-condyloid fossa, descends between the two portions of the 

 gastrocnemius — to the external of which it is intimately related — on the posterior 

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

 muscles. On reaching the inferior extremities of the muscular bellies of the 

 gastrocnemius, 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 completely envelops in order to be fixed on its lateral 

 portions, and is united to the calcanean 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 metacarpus 

 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. 



Beep Layer. 

 4. PoPLiTEUS (Fig. 203, 21). 



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



Situation — Direction — Form — Structure. — Situated behind the tibia, below 

 the femoro-tibial articulation, this muscle is oblique downwards and inwards, 

 short and triangular, tendinous at its supero-external angle, and formed, for the 

 remainder of its extent, of divergent fleshy fibres, the longest of which are the 

 most inferior. 



Attachments. — 1. In the lowest of the two fossae on the outside of the external 

 condyle of the femur, by its tendon — origin. 2. On the supero-posterior trian- 

 gular surface of the body of the tibia, by the inferior extremity of its muscular 

 fibres — termiyiation. 



Relations. — Posteriorly, with the gastrocnemius and perforatus. In front, 

 with the posterior ligament of the femoro-tibial articulation, and the pophteal 

 vessels. Outwards, with the oblique and deep flexors of the phalanges. Inwards, 

 with the semitendinosus and tibial aponeurosis. The tendon, concealed at its 

 origin beneath the external femoro-tibial ligament, glides, by its deep face, over 



