PHYSIOLOGY OF MOVEMENT. 



759 



on their wing-cases, or their wing-cases on each other or on the thorax 

 or abdomen. In humming insects sound may be produced by forcing 

 the expired air from their stigmata, which are provided with muscular 

 rods and which are thus thrown into vibration, so that in this group of 

 insects, represented by the humming-bees and many dioptera, the closest 

 analogy exists between the production of sound and the production of 

 voice in the vertebrates. 



IB 



Libr 



L.ibr 



FIG. 315. INFERIOR LARYNX OF THK TURKEY. (Griitzner.) 



A, during voice production : B, in free respiration. (In At and J5' the anterior wall is removed.) 

 m.st.tr., sterno-tracheal muscles in contracted condition in A and A> ; Tr., trachea; v, Tr. R., 

 united tracheal rings, forming the tympanum with its antero-posterior bridge, S. ; B. Sp., bronchi ; m. t. ., 

 external tympanic membrane ; m. 1. 1.. internal tympanic membrane stretched out flat in B and Bf, in A 

 and Al forming sharp folds in the lumen of the bronchi; L. ibr., interbronchial ligament; b., band run- 

 ning to the dorsal wall of the trachea. 



Animals below insects, as radiates and mollusks, are all entirely 

 incapable of sound. Among reptiles, certain of them, such as frogs, 

 lizards, and other batrachians, possess true vocal organs. Among am- 

 phibians the frog has a larynx provided with muscles, which produces a 

 sound of varying pitch, dependent upon the strength of the muscular 

 contraction and the force of the expiratory blast. The range of such 

 vibrations is, however, extremely limited. In the Rana esculenta there 

 is on each side of the angle of the mouth a membranous bag which may 



