440 



Mr. W. P. Herringham. 



epiblastic layer which forms the skin ensheaths the mesoblast, from 

 which the deeper structures are developed. Suppose nerves, or what 

 will afterwards become nerves, to be distributed to both. The meso- 

 blast now begins to grow and pushes before it the enveloping sheath 

 of epiblast. But, as may be seen with a piece of india-rubber, in any 

 such process the points furthest from the centre of pressure remain 

 nearest the top of the tube, and the point which was in the middle 

 when the stretching began, will be at the furthest point of the sheath 

 when it is finished. If in the arm the centre of pressure be supposed 

 opposite to the area supplied by the 7th nerve, this nerve will always 

 tend to supply the parts lying nearest the axis of the limb, and 

 furthest from the axis of the body, while the 6th, 5th, and 4th in the 

 pre-axial, and the 8th, 9th, and 10th in the post-axial area, will in that 

 order approach the trunk. This is the case. 



It appears then that in both sensory and motor systems the pre- 

 axial area is supplied by higher nerves, the post-axial by lower ; that 

 the supply of the skin follows rules which obtain in any membrane 

 subject to the same conditions, but that the supply of the muscles is 

 modified by laws peculiar to themselves. 



This subject has not to my knowledge been before this investigated 

 by human dissections. 



Ferrier's* classification of the muscles by means of electric stimula- 

 tion of the spinal roots in monkeys, though he explains the system as 

 one of function, is not far removed from that now put forward. 



Forgue,f who stimulated not the spinal roots, but the branches 

 which they gave to the nerves of the plexus, and who watched the 

 contraction of dissected muscles, draws up the following list for 

 monkeys : — 



Median. "I 



f 5 and 6 / -^ ce P s - Brachialis anticus. Clavicular part of 

 Median J I deltoid. Pronator teres. Flexor carpi radialis. 



externe. \ j f Biceps slightly. Pronator teres. Flexor carpi 

 1 radialis. 



M 'dian ] f ^ >rona ^ 01 ' teres and flexor carpi radialis slightly, 



interne J ^ ^ ] flexor sublimis. Flexor profundus. Flexor 

 I carpi ulnaris. Intrinsic muscles of hand. 



* 1 Koy. Soc. Proc.,' vol. 32, 1881, p. 12. 



f 'Distribution des Eacines Motrices dans les Muscles des Menibres.' Hlmile 

 Forgue. Montpellier, 1883. Page 45. 



X Forgue's median is both median and musculocutaneous. Median externe is 

 the musculo-cutaneous and the outer head of the median, median interne the inner 

 head. 



