'308 Mr. Yarii^ll on the Organs of Voice in Birds. 



cal, or triangular at its lower surface, (Tab. XVII. Fig. 7, 11, 

 & 12) having a central cross-bone extending from behind to the 

 front, dividing the orifice in two equal parts (Fig. 11 & 12, a, a) ; 

 to the outer side of which cross-bone the inner membrane of 

 each bronchial tube is attached. This cross-bone thus dividing 

 the lower orifice, forms the point of divarication from which the 

 bronchiae arise separate, and go off to the lungs. But a more 

 minute description of this important part will be given, when 

 considering the various muscles connecting the bone of divari- 

 cation with the bronchise. 



The bronchiae are formed on the outer sides by membrane 

 interposed between and connecting a variable number of carti- 

 lages which describe only parts of circles, diminishing in size as 

 they approach the lungs, the circle being completed on the 

 inner side by a delicate membrane stretching from the opposite 

 points of the semicircular cartilages, and forming a tube from 

 the orifice of the inferior larynx to the substance of the lungs 

 (Tab. XVII. Fig. 9 & 10, c, c). This membrane is called by 

 Cuvier the membrana tympaniformis, and upon its dilatation and 

 contraction, as well as the power afforded of altering the form 

 and length of the bronchiae, some of the varieties of intonation 

 depend. The bronchiae are also slightly attached to each other 

 and to the oesophagus. 



The muscles of the glottis or superior larynx are uniformly 

 two pair in all the birds I have examined : but the muscles 

 of the inferior or true larynx, all largely supplied with nerves, 

 vary from one pair to five pair, according to the genus or spe- 

 cies, affording a corresponding increase in the various qualities 

 of the voice. Some few birds have no true muscles of voice at 

 the inferior portion of their tracheae. Cuvier describes the 

 King of the Vultures as being without any ; and this is also the 

 case with the Condor. Tab. XVII. Fig. 5. is a representation 



of 



