256 On the Minute Anatomy of the Brachial Plexus, [Mar. 25, 



The internal and lesser internal cutaneous are usually supplied by the 

 9th, the former occasionally by the 8th as well. 

 The posterior branches : — 



The subscapulars is supplied by branches from the 5th and 6th 

 only ; the teres major by the 6th, often with a twig from the 7th ; the 

 latissimus dor si by the 7th, often with a twig from the 8th. 



The circumflex is formed by the 5th and 6th. The latter is not 

 traced to the teres minor. Both go to the deltoid. The cutaneous 

 branch is formed by the 5th alone, or by both. 



The musculo spiral is formed by the 6th, 7th, and 8th ; sometimes 

 the 5th, and rarely the 9th, send branches to it. 



The triceps is supplied by the 7th and 8th. The long head usually 

 by the 8th, the inner head by the 7th and 8th, and the outer by the 

 7th. The 6th sometimes runs to the outer head. 



The internal cutaneous branch comes from the 8th. The short 

 external cutaneous springs from the 6th, the long varies round the 

 7th. The brachialis anticus, supinator longus, and supinator brevis 

 are supplied by the 6th. 



The extensor carpi radialis longor and brevior are supplied by the 

 6th or 7th, usually the latter. 



The radial is supplied by the 6th alone, or by the 6th and 7th. 



The posterior interosseous is usually from the 7th alone, sometimes 

 with aid from the 8th. 



The nerves, both sensory and motor, are shown to obey the follow- 

 ing law : — 



I. Any given fibre may alter its position relative to the vertebral 



.column, but will maintain its position relative to other fibres. 



An exceptional case is detailed in exemplifying this law. 

 The muscles are classed in a table, according to their motor nerve 

 supply. 



The system of the motor supply appears to be not according 

 to use, but according to position, morphological not functional, and 

 obeys the following law, composed of three rules : — 



II. A. Of two muscles, or of two parts of a muscle, that which is nearer 



the head end of the body tends to be supplied by the higher, 

 that which is nearer the tail end by the lower nerve. 



B. Of two muscles, that which is nearer the long axis of the body 



tends to be supplied by the higher, that which is nearer the 

 periphery by the lower nerve. 



C. Of two muscles, that which is nearer the surface tends to be sup- 



plied by the higher, that which is further from it by the lower 

 nerve. 



These rules are applied in detail. 



