635 



Tims it results lliat tlie Iriiuk-skiii of (lie dog forwards its stimuli, 

 destiued for a definite segment of the spinal cord, only by means 

 of one set of perij)herioal skin-nerves. This means that in those 

 nerves only fibres belonging to one posterior root have their course, 

 and that consequently the perforating skin-branches are segmental 

 nerve-canals. 



II. A second question, necessarily presenting itself, is the following 

 one: what separate portion within the dermatoma is innervated by 

 either the dorsal or the lateral (ventral) peripherical branches? 



To investigate this, the above-mentioned method was partially repeated 

 once more. With dogs, where a nerve-root had been isolated, the 

 peripherical branches enterlaining its sensibility were sought for and 

 prepared free. After this the conduction was successively interrupted, 

 either provisorily or lastijiglj', in one or more of these branches. 

 To obtain a lasting interruption of the conduction, the l)ranch was cut 

 through. For a provisory interruption the branch w^as enfolded by a 

 piece of cottonwool, drenched in a 5 7o solution of stovaine. The 

 conduction once interrupted, the root-area was tested to ascertain 

 whether a portion of it had become insensible, and if so the confines 

 of the insensible area found in this manner were determinated. 



Fig. 3. On a dog a root-area (Th. 10) has been isolated between two 

 insensible zones. After this, three cutaneous branches belonging to the dorsal 

 perforating nerve-trunk, are successively cut through. The dotted portion 

 of the root-area then becomes successively insensible, until finally the whole of 

 its dorsal part has lost sensibility. 



a. Interruption of the conduction in the joint dorsal cutaneous 

 branches. 



