387 



CniiD.S 



AOULT.S 



downwards so that at the time of birth the nerve has an inverted 

 U-shaped course over the first rib. Any influence therefore which 

 provokes an extensive dropping of the shoulder will tend to stretch 

 this nerve over the upper surface of the first rib and will provide 

 the mechanical condition necessary to produce the pressure usually 

 associated with symptoms cervical rib. 



In consequence of 

 this tendency 1 thought 

 that the descent of the 

 shoulder from infancy 

 to adult age might 

 stretch the lowest bra- 

 chial trunk over the first 

 rib in certain cases, as 

 is represented in the 

 hypothetical drawing, 

 Fig. I. In this illustra- 

 tion the arrow-head re- 

 presents the point of 

 pressure of the first rib 

 on the nerve. 



A and A' represent 

 the corresponding points 

 of the nerve in child- 

 hood and in adult life, 

 to show how descent of 

 the shoulder might assist 

 in the production of 

 symptoms commencing 

 in early adult life. I there- 

 fore obtained measure- 

 ments of the angle be- 

 tween the direction of 

 the clavicle and the 

 horizontal in both sexes 

 and at various ages from 

 3 years upwards. The 

 clavicular angle may be 

 measured by placing 



MIC 



Fig. IL 



Fig. I. Hypothetical diagram to illustrate the 

 descent of the shoulder (S) in growth from infancy to 

 adult age. The clavicle (thick black line) is represented 

 as if its inner extremity were fixed, as was thought 

 possible at the beginning of the present research. The 

 arrow head represents the site of pressure on the nerve 

 (outlined only) by the first rib. In this diagram I have 

 attempted to show how the descent of the shoulder 

 would tend to stretch the nerve over the first rib, were 

 it not that the influence of the descent of the first 

 rib compensates the descent of the shoulder. 



Fig. 2. Diagram to show the clavicular angle : 

 This is the angle which the clavicle makes with the 

 horizontal. The clavicular angle seems to be exaggerated 

 in the drawing. This is because the angle is actually 

 measured in an oblique manner, and is greater than 

 the true vertical elevation of the bone (see text). 



25* 



