v SPINAL COED AND NERVES 301 



fact the spinal nerves intermix so freely along their course in the 

 plexuses (cervico-dorsal, lumbo-sacral plexuses) that it is necessary 

 in order to ascertain the peripheral distribution of each sensory 

 and motor root to resort to the embryological method, or the 

 physiological methods of section and excitation, or the pathological 

 method of degeneration combined with clinical observations. 



Apart from observations by the older anatomists (Eeil, Monroe, 

 Scarpa, Sommering), Schroder van der Kolk (1847) was the first 

 to occupy himself with the peripheral distribution of the spinal 

 roots. He assumed that the branches of the mixed nerves in 

 general are distributed so that the sensory ramifications terminate 

 in the region of the skin lying immediately over the muscles 

 innervated by the motor fibres of the same nerve. 



Starting from this concept, Eckhard (1849) studied on the frog 

 the relations between the peripheral terminations of the dorsal and 

 ventral roots that innervate the hind-limbs. He found Schroder's 

 law to be true, but not entirely accurate, since the sensory fibres 

 do not exactly supply the cutaneous areas over the muscles 

 innervated by the corresponding motor fibres. In order to discover 

 the distribution of the sensory roots in the skin, he divided all 

 the dorsal roots save one, and then ascertained which area of 

 the skin still preserved its sensibility. In this way he dis- 

 covered that each root provides sensibility to a definite and 

 continuous region of the skin, and that these regions more or less 

 overlap one another. To determine the distribution of the motor 

 roots, he experimented with electrical excitation of one alone, after 

 section of the rest, and found that it only threw certain of the 

 muscles of the limb into contraction. This corrected an observa- 

 tion made by Kronenberg (1836) under Johannes Muller's 

 direction. He attributed to the plexus a protective function 

 against fatigue, and assumed that the stimulation of a single root 

 forming part of the plexus was able to throw all the muscles of 

 the limb into contraction. 



Eckhard's results were controlled by Koschewnikoff (1868), C. 

 Mayer (1869), and more recently by Sherrington (1893), without 

 substantial modification. Peyer (1854) and Krause (1865) 

 obtained similar results on the rabbit. 



But in all these researches the leading motive that was to 

 combine the scattered facts into one system was wanting, viz. the 

 extension of the idea of segmentation metamerism to the peri- 

 pheral distribution of the sensory and motor roots. Tiirck (1856) 

 first detected a segmental arrangement in the cutaneous areas 

 supplied by the sensory roots. He divided the dorsal roots one by 

 one in the dog, and determined the peripheral distribution of each 

 by observing the zone of insensibility to touch and pain that 

 ensued in the skin. He thus discovered the cutaneous root areas 

 for the whole of the dog's body, and showed that a part of each 



