MUSCULAR SYSTEM 



D 



All anthropologists are agreed that man alone possesses the 

 power of giving animated and varied expression to the mouth 

 and eyes, and that he owes this power to the perfection of the 

 above-mentioned muscles. Progressively modified are the 

 muscles of the hand, particularly of the index finger and thumb. 

 The extensor of the index finger, of which the anthropoids 

 have but a mere suggestion (in the gorilla) ranks as the 

 specifically human muscle, par excellence, on account of the 

 power of gesticulation it bestows. 



The flexor proper of the thumb (m. flexor pollicis long, 

 propr.) is also thoroughly de- 

 veloped in man alone. In 

 most human subjects the two 

 flexors of the fingers (m. flex, 

 dig. comm. subl. and m. flex, 

 digit, comm. prof.) are sepa- 

 rated in such a manner that 

 the four tendons of the pro- 

 fundus are inserted through 

 slits in the four tendons of the 

 sublimis. When this is not the 

 case, the conditions are similar 

 to those prevailing in many of 

 the mammals ; for instance, in 

 most of the apes (see Figs. 44 

 and 45). 



The great muscle of the 

 lower extremity in man, the 

 gluteus maximus, so superior 

 to the corresponding muscle in the anthropoids, owes its massive 

 formation and progressive development to its influence on 

 the erect position. The gastrocnemius and soleus with their 

 insertion into the calcaneum exhibit similar distinct human 

 characters. 



In conclusion we may mention the flexor of the great toe 

 (m. flex, hallucis long.) as another characteristic acquisition of 

 progressive development (see Figs. 46, 47, 48). 



If we compare the gorilla, the highest of the anthropoids, 

 with man we are immediately struck by the formation and 



FIG. 43. Facial muscles of mimicry. 

 (Henle.) C, orbicularis palpebra- 

 rum ; D, pyramidalis nasi ; E, 

 levator labii sup. ; F, levator labii 

 prop.; G, zygomaticus; I, zygo- 

 maticus minor ; K, triangularis 

 oris; M, risorius. 



