MUSCULAR SYSTEM 



111 



and the frequent absence of that to the fifth toe, evidences of a 

 retrogressive tendency. 



The special extensors of the fingers undergo similar variations, 

 being now as a rule restricted to 

 the thumb, the index, and the 

 little fingers. Occasionally, how- 

 ever, the third and fourth fingers 

 also receive tendons from the ex- 

 tensor minimi digiti,andthe middle 

 finger may receive a tendon from 

 the extensor indicis proprius. 



The changes brought about in 

 the sole of the foot naturally affect 

 the dorsum as well. There can 

 indeed be no doubt that changes 

 have taken place in the extensor 

 brevis digitorum of the foot (e.br., 

 Fig. 72) complementary to those 

 above described in the flexor digi- 

 torum communis brevis. The 

 extensor brevis digitorum must 

 formerly have arisen higher up 

 the fore-leg, and have secondarily 

 shifted downwards to the dorsum 

 pedis. The connection demon- 

 strated by Euge between the short 

 common flexor of the toes and the 

 interossei pedis undoubtedly in- 

 dicates the " extreme limit of the 

 distal wandering of the extensor 

 brevis." 



Euge has further proved the 

 interesting fact that all the seven 

 interossei pedis at a certain stage 

 in the human embryo have a 

 plantar disposition, and that they 

 shift at a later stage to a position 

 between the metatarsals, there to 

 divide into the plantar and dorsal 



series. An exact parallel to this is found in certain Apes (Cebus, 

 Cercopithecus) and in most of the lower Mammals, in which 

 the interossei have a plantar position throughout life. In the 



2. SUPERFICIAL MUSCLES AND 

 TENDONS OF THE DORSUM OF THE 

 RIGHT FOOT. One -third natural 

 size'. (After Rauber.) 

 tibia ; b, fibula ; c, navicular ; t.a'., 

 tibialis anticus muscle ; t.a"., its 

 tendon of insertion ; e.l'., M. extensor 

 hallucis (e.hall. long.) i ; e.d'., 

 extensor communis digitorum 

 (e. digit, longus) ; e.d"., its expan- 

 sion and insertion on the second toe ; 

 p.f., peroneus tertius ; p.t"., its 

 insertion on the fifth metatarsal 

 bone; *., M. soleus ; p.b., M. 

 peroneus brevis ; e.b., M. extensor 

 hallucis brevis ; e.br., extensor brevis 

 digitorum ; Ig. anterior annular 

 ligament ; fc., transverse band of 

 the dorsal fascial of the foot. 



