302 THE MUSCLES. 



in front of the superior extremity of the principal metatarsal bone, along 

 with the analogous branch of the tendinous division (Fig. 136, 8). The 

 other ramification is directed to the inside of the tarsus, to be attached to 

 the second cuneiform bone (Fig. 136, 7). 



Relations. In front, with the tendinous portion of the muscle and the 

 anterior extensor of the phalanges ; behind, with the external face of the 

 tibia. The tendon, after traversing the annular ligament of the cord, covers 

 the metatarsal branch of the latter, and is in turn covered by the anterior 

 extensor. 



Action. It is an active agent in flexing the foot on the leg. 



B. Posterior Tibial Region. 



This region comprises six muscles, which are arranged in two super- 

 posed layers behind the tibia. The superficial layer is formed by the 

 gastrocnemiij soleus, and the superficial flexor of the phalanges. The deep 

 layer is composed of the popliteus, the deep flexor, and the oblique flexor of 

 tlw phalanges. 



1. Gastrocnemii, or Gemelli of the Tibia. (Figs. 135, 22 ; 137, 20.) 

 Synonyms. Bifemoro-calcaneus Girard. ( Gastrocnemius externus PercivalL) 

 Situation Composition Extent. The gemelli of the leg, situated behind 

 the femoro-tibial articulation, below the ischio-tibial muscles, constitute 

 two thick 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 calcis. 



Form Structure. 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 aponeu- 

 rosis, p. 297). An aponeurotic lamina which covers the external gemellus, 

 is continued downwards, partly with this 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 in front the supracondyloid fossa ; 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 calcis, not at its anterior part, but posteriorly, this being lubricated by a 

 vesicular synovial membrane forming a gliding surface on which the tendon 

 rests during extreme flexion of the foot (Fig. 67, 1). 



Relations. The gemelli respond : by their superficial face, to the three 

 ischio-tibial muscles, and the tibial aponeurosis; by their deep face, to 

 the perforatus, which contracts intimate adhesions with 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 per- 

 foratus, which is twisted around and completely envelopes it at its inferior 

 extremity, in common with the fibrous band from the tibial aponeurosis. 

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

 tendon of Achilles, 



