Royal Society. 4.5 1 



Sir Charles Bell's paper "On the Organs of the Human Voice" was 

 then read in continuation. 



February 16. — The reading of Sir Charles Bell's paper " On the 

 Organs of the Human Voice," was resumed and concluded. 



The author complains that the actions of the organs of the voice 

 have been negligently treated by physiologists, and that manj' of 

 the offices of the structures subservient to that function have been 

 overlooked ; and expects that the study of them will lay a founda- 

 tion for prosecuting the intricate anatomy of the nerves of the 

 neck, which he proposes to himself as an ulterior object. The 

 subjects to which he particularly directs his attention in the present 

 paper, are the Muscularity of the Trachea, the Position of the 

 Thyroid Gland, and the Action of the Pharynx, which he alleges to 

 have been entirely omitted in previous systematic accounts of 

 articulate language. 



The trachea is strengthened by imperfect circles of cartilage, 

 the ends of which are united at the back part of the tube by a 

 transverse layer of muscular fibres, — a structure which is very dis- 

 tinctly seen in the horse. This transverse muscle is an antagonist 

 to the elasticity of the cartilages, and the effect of its action during 

 expiration is, by contracting the diameter of the tube, to favour the 

 propulsion of the mucous secretion, which may have been accumu- 

 lated in the passage, and to contribute effectually to expel it by the 

 effort of coughing. The same action leads also to the expulsion 

 of foreign bodies which may have accidentally got into the trachea. 

 In birds, where the inner surface of the passage is without moist- 

 ure, no such provision was required ; and accordingly we find the 

 cartilages of the trachea are complete circles, not admitting of con- 

 traction. 



The author considers the thyroid gland as serving the purpose 

 of interrupting the vibrations of the cartilages of the trachea, to 

 which it is closely attached, especially when pressed against it by 

 the actions of the flat muscles which extend over it. If sound 

 were given out by the vibrations of the trachea, it would interfere 

 with the distinctness of the voice. The thyroid gland is, therefore, 

 placed low in the larynx, and on the upper part of the trachea, for 

 the purpose of checking the vibrations of that tube, and suppress- 

 ing the sounds that would thence he produced. In birds, where 

 the voice originates in the inferior larynx, and is propagated along 

 the trachea, the structure of that tube is adapted to vibration, the 

 circles of cartilage being complete, and there is no thyroid gland. 



In man, the primary source of the voice is the vibration of the 

 chordae vocalcs, or ligaments of the glottis, acted upon by the im- 

 pulsion of the air passing by them. The proper degree of tension 

 is given by these ligaments by the action of the muscles, which 

 adjust their position with the greatest accuracy. The movements 

 of the chest, which regulate the expulsion of the air, are at the 

 same time adapted with great nicety to the production of the re- 

 quired ett'ect. The sacculi laryngis also contribute to give greater 

 extent and freedom to the vibrations of the glottis. It is by the 

 3 M 2 concurrent 



