RAVEN. 73 



dividing the orifice into two equal parts ; to the outer side of 

 which cross-bone the inner membrane of each bronchial tube 

 is attached. This cross-bone, thus dividing the orifice, forms 

 the point of divarication from which the bronchise arise sepa- 

 rate, and go off to the lungs. But a more minute descrip- 

 tion of this important part will be given, when considering 

 the various muscles connecting the tube, the bone of divari- 

 cation, and the bronchise. 



The bronchial tubes are formed on the outer sides by 

 membrane interposed between, and connecting a variable 

 number of cartilages which describe only parts of circles, di- 

 minishing in size as they approach the lungs, fig. 2, c, the 

 circle being completed on the inner side by a delicate mem- 

 brane stretching from the opposite points of the semi-circular 

 cartilages, fig. 8, c, and forming a tube from the orifice of the 

 inferior larynx to the substance of the lungs. This mem- 

 brane is called by Cuvicr the mevihrana tyvipaniformis, and 

 upon its dilatation and contraction, as well as the power af- 

 forded of altering the form and length of the bronchioe, 

 some of the varieties of intonation depend. The bronchise 

 are also slightly attached to each other, and to the oeso- 

 phagus. 



The muscles of the glottis, or superior larynx, are uni- 

 formly two pair in all the birds I have examined ; but the 

 muscles of the inferior, or true larynx, all largely supplied 

 with nerves, vary in number from one pair to five pair, ac- 

 cording to the genus or species, affording a corresponding 

 increase in the various qualities of the voice. 



Some few birds have no true muscles of voice at the infe- 

 rior part of their trachese. The Vultures, — some of them at 

 least, — are described as being without any. No. 1 is a re- 

 presentation of the lower portion of the trachea of a Vulture, 

 without muscles, or any true bone of divarication, the bron- 

 chial rings almost completing the circle, with little flexibility. 



