395 



Results. 

 The observations embodied in the present paper appear to justify 

 the following conclusions: — 



(1) Symptoms of 'cervical rib' may be caused by an apparently 

 normal first dorsal rib, and may be cured by its removal. 



(2) To explain the mechanical pressure caused by the first rib on 

 the lowest brachial trunk, it is necessary to consider the descent 

 of the clavicle after birth. 



(3) Two factors are at work in the descent of the clavicle. They 

 act at each end of the bone without reference to each other. 



(4) The factor producing descent of the inner end of the clavicle 

 is the tilting downward of the anterior end of the first rib. 

 This is produced to a large extent by the tonic traction of the 

 recti abdominis muscles on the sternum. 



The descent of the inner end of the clavicle is somewhat 

 greater in men than in women. 



(5) The descent of the shoulder proper can only influence the outer 

 end of the clavicle, and it is modified by the degree of develop- 

 ment of the muscles. The outer end of the clavicle descends 

 somewhat further in women than in men. 



(6) The angle which the clavicle makes with the horizontal results 

 from the independent action of the forces mentioned in (4) 

 and (5). 



(7) In consequence of the action of these forces, pressure symptoms 

 on the lowest brachial trunk are most likely to occur in women 

 at the commencement of adult age. 



References. 



(1) Murphy: Australian Med. Journ. Oct. 1910. 



(2) Todd: Costal Anomalies of the Thoracic Inlet. Anat. Anzeiger May 18tli,1912. 



(3) Ibid. The relations of the Thoracic Operculum. Journ. Anat. and Phys. 1911. 



(4) Ibid. Cervical Eib. Journ. Anat. and Phys. 1912. 



(5) Mosso: Les Movements respiratoires du Thorax et du Diaphragme: Arch. 

 Ital. de Biol., t. XL, 1903. Quoted by Keith in The Mechanism of Respira- 

 tion in Man. Further Advances in Physiology, 1909. 



(6) Pasteau : Pecherches sur les proportions de la Clavicule dans les sexes et 

 dans les races. Quoted by Poirier. Poirier et Charpy. Traite d' Anatomie : 

 3rd edit., 1911, tome I, p. 424. 



(7) Desvernine, a contribution to the study of the oral extremity of the 

 thorax. New York, Med. Journ., April 6, 1912. 



