i68o 



II WDllllOK UK PHYSIOLOGY 



M I KOI'HYSIOLOGY III 



elongated body while the entire posterior part con- 

 sists of organs <>l locomotion enclosing ilic v isceral 

 c.iv ity. 



It is in this cephalic area, served by the apparatus 

 of prehension, that the first forms of specialized 

 technical activity will develop. The major use oi 

 these technical operations is at first alimentary in 

 character: the capture of prey, its seizure and the 

 dissection ol" the food. 



The appearance of locomotor appendages sym- 

 metrically disposed along a longitudinal axis is soon 

 accompanied by adaptation of the most anterior 

 elements of this mechanism to aid the organs of pre- 

 hension of the buccal region. 



The evolution of vertebrates, and especially that 

 ol mammals, is marked by a simultaneously synergic 

 and competitive interpenetration of the motor ap- 

 paratus of prehension and that of locomotion. Thus, 

 in the herbivorous mammals, the anterior members 

 lose all integration with the cephalic region. This 

 fact seems to favor the development of facial tools: 

 the ruminants' specialized incisors, the elephants' 

 tusks, nasal and frontal horns, extensive lips, trunks, 

 etc. 



Other mammals, on the contrary, which have 

 kept the live-fingered hand of the primitive reptiles 

 use the anterior members for technical purposes. 

 This appears in various stages of development in a 

 great number of species, the functional organization 

 in which is often without direct relation to their 

 taxonomic positions. Each group offers examples of 

 species utilizing the anterior members for technical 

 purposes. The least favored are the species spe- 

 cialized fur rapid locomotion as, for instance, the 

 hare as compared with the heaver among the rodents. 

 IIk- technical use of these anterior locomotive ap- 

 pendages l>v these species is accompanied liv .1 

 particular postural evolution, the acquisition of a 

 sitting position which liberates the .interior members 

 and facilitates their technical activity (log). 



The most f.ivoied .ire ihe prim. lies which show 



the highest level of appendicular technical facility. 



The particular form of locomotion that is imposed 

 Or) the monkey l>v arboreal life i* .leeompanied hv a 



transformation oi the four extremities into perfected 

 .us iii prehension; as Broca (18) remarked, "The 



monkev is more a quadruui.in than a quadruped." 



The tail itself becomes a real organ of prehension. 

 Conjointly with this evolution ol appendicular tech 



nieal skill, there has been progressive erection of (he 

 vertelir.il column in the sitting position. 



The essential feature marking the transition from 



the monkey to man is the locomotive arrangements 

 of the latter. The human foot presents an evolution 

 of the same order as that of the quadruped mammals 

 which use their four limbs exclusively for rapid loco- 

 motion. In contrast, the hand evolves definitely in 

 the prehensile sense. 



Thus this evolution is marked, from the anatomical 

 point of view, by a definite liberation of the anterior 

 members from servitude to locomotion by the erec- 

 tion of the vertebral column to the vertical position. 

 The gain in power of the hand brings about a parallel 

 regression of the organs of facial prehension. The 

 skull is then liberated from its duties of mechanical 

 support for the apparatus of mastication on the 

 vertebral column. It may then increase in size (71). 

 From the functional point ol view, this evolution 

 results in the nearly total predominance of the hand 

 in technical acts, a nearly complete liberation of the 

 buccal organs so that they may become available 

 for the development of new motor mechanisms of 

 expression, and an increase in the volume of the 

 brain in an enlarged cerebral cavity. 



The neuromotor system has evolved in relation to 

 this change in body relations. Whereas the locomo- 

 tive functions have remained dependent upon sub- 

 cortical centers, the development of motor activities 

 of technical character appear to have been intimately 

 associated with expansion of the motor anas in the 

 neocortex. 



In the species in which facial behavior is promi- 

 nent, there exists an extensive cortical sensorimotor 

 'representation' of the anterior facial region. The 

 progress of the technical proficiency of the anterior 

 locomotive appendages is accompanied hv a progres- 

 sive extension of the cortical sensorimotor representa- 

 tions of these regions, particularly for their distal 

 parts. Ihe area and the density of the corresponding 

 cellular fields increase in proportion to the cora- 

 plexiiv and the delicacy of the movements which 

 they control. The largest fields correspond to the 

 organs most frequently engaged in technical opera- 

 tions: ihe lips, the tongue and (he distal portions "1 

 (In- anterior limbs ( 1 . |8, 136) 



In the monkey, ihe 'representation' of the digits 



(notably (he thumbs) and of the tail lake on con- 

 siderable importance. Man possesses an extensive 

 'representation' of (he hand, with predominance of 



ihe thumb, then oi the second and die fifth digiis, 

 whereas the inferior membei is poorly 'represented,' 



as shown in figure I . 



Ii is significant in notice here that, in spite of the 

 apparent regression ol facial technical capacity in 



