Posterioi 



THE BRACHIAL PLEXUS 97 



f 



(Upper (Short) Subscapular (C. 5 and 6). 

 Lower (Middle) Subscapular (C. 5 and 6). 

 Thoraco-dorsal (Long Subscapular) (C. 6, 7, and 8). 

 Radial (Musculo-Spiral) (C. 5, 6, 7, and 8). 

 Axillary (Circumflex) (C. 5 and 6). 



Lesions of the plexus or of its constituent parts are followed 

 by alterations in the motor and sensory functions in the area 

 supplied. It must be remembered that the areas supplied by 

 cutaneous nerves overlap one another to a considerable extent, 

 and that section of a single cutaneous nerve will produce an area 

 of altered sensibility which is much smaller than the area of 

 anatomical supply of the nerve involved. 



Note. Three varieties of sensibility are described by Head and Sherren. 

 (i) Deep Sensibility. This form of sensation is conveyed by fibres which 

 run with the motor nerves and associate themselves with muscles, tendons, 

 periosteum, and ligaments. By these fibres coarse tactile stimuli are recog- 

 nised even after division of cutaneous nerves. Deep sensibility disappears 

 when a nerve is cut proximal to the origin of its motor branches, or when the 

 tendons, which convey the nerve fibres, are severed. (2) Protopathic 

 Sensibility. Painful cutaneous stimuli and extremes of temperature are 

 recognised by this form of sensibility, which is conveyed by the cutaneous 

 nerves. The areas of protopathic supply by different nerves overlap one 

 another to a considerable extent. (3) Epicritic Sensibility. This form 

 of sensation, which is also conveyed by the cutaneous nerves, responds to 

 light touch, localises accurately all painful and tactile stimuli, and recognises 

 intermediate degrees of temperature. 



For a full and complete discussion of the various forms of sensation 

 the reader is referred to the works of the authors referred to above. 



Lesions of the Supra-clavicular Branches. The Long 

 Thoracic Nerve (of Bell) (C. 5, 6, and 7) and the Dorsalis 

 Scapulae Nerve (to the Rhomboids) (C. 5) both arise so close 

 to the inter vertebral foramina that they are rarely injured in 

 tears of the plexus. The latter nerve may be injured in removal 

 of lymph glands from behind the posterior belly of the omo- 

 hyoid,, unless the pervertebral fascia on the floor of the posterior 

 triangle of the neck is left intact (p. 135). In paralysis of the 

 rhomboid muscles the scapula on the injured side lies slightly 

 lower than it should; and the inferior angle is at a greater distance 

 from the median plane than it is on the sound side. 



The Long Thoracic Nerve (of Bell) (p. 131) may be injured 

 in operations involving the axilla (p. 35) or by the pressure of 

 weights carried on the shoulder. In the latter case the dorsalis 

 scapulae nerve (to the rhomboids) and the branches of C. 3 and 

 C. 4 both motor and sensory which cross the posterior triangle 

 of the neck (p. 126), may also be injured. Owing to this com- 



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