MEDICAL BATTERIES. 85 



part of the muscular tissue behind the deep surface of which they 

 are concealed. This, however, does not prevent the current from 

 penetrating to them, when such an action is required. 



An exact knowledge of the points of emergence and immersion 

 of the muscular nerves is absolutely necessary in order to study 

 the proper action or the state of the properties of muscles, or 

 of those fasciculi which, physiologically considered, are often 

 distinct muscles themselves. At the beginning of my researches, 

 I found it a matter of the greatest difficulty to limit exactly the 

 action of tlie current to each muscular bundle, because I did 

 not possess the knowledge. It was necessary to commence new 

 anatomical studies, in order to determine, as exactly as possible 

 (because in this respect there are certain individual differences), 

 the points of exit and of entrance of the nerves ; and by these I 

 learnt to avoid the nerves, when I wished to excite single fasciculi ; 

 and to excite them, when I wished to obtain the contraction en 

 masse of large muscles or fasciculi. 



It is not always sufficient, however, to be able to avoid the 

 points of exit or of entrance of the nerves, in order to obtain 

 the isolated contraction of one of the bundles of a muscle. There 

 are certain points of election on which the rheophores should be 

 placed ; and which must be sought in order to be perfectly known. 

 I will take as an example the extensor communis digitorum. In 

 a person in whom the forearm measures twenty-four centimetres 

 from the olecranon to the styloid, process, the point of emergence 

 of the nerve is, as a rule, six centimetres from the epicondyle. 

 Before dividing, the nerve has a length of two centimetres ; and 

 its point of immersion is at twelve centimetres below tlie epicon- 

 dyle; it being then divided into two branches. With these 

 anatomical data, it is evident that a rheophore of small surface 

 placed over the nerve prior to its division, — that is, over the central 

 part of the extensor communis at a point between six and eight 

 centimetres below the epicondyle, — will produce simultaneous con- 

 traction of all the fasciculi of the muscle, if the current be suffi- 

 ciently penetrating to reach the nerve. But at twelve centimetres 

 below the epicondyle (the point of immersion) the rheophore must 

 fee brought into relation with two branches in order to produce the 

 same eiiect. In other words, the rheophore must either cover a 

 large surface, or only one of the branches v.ill be excited, and only 

 two fasciculi will be thrown into contraction. 



If it be desired to obtain isolated contraction of each fasciculus 

 of the extensor communis, it will evidently be necessary to avoid 

 the nerve before its division, and to seek the points at which the 

 muscular fibres constituting each fasciculus become sul; cutaneous. 



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