270 CORVID^. 



and convey the food to the gullet, or oesophagus, and hinder 

 its return so as to enter the windpipe. This orifice is 

 hounded on either side hy the arytaenoid cartilages, seen 

 more plainly in Fig. 2 {b, h), where the greater part of the 

 cricoid cartilage {a, a, a) has been removed, together with 

 the investments of the windpipe (c), that the bony rings of 

 which this is composed may appear more clearly. Figs. 3 

 and 4 illustrate the muscles which control the size of the 

 orifice, and constitute one of the accessory means by which 

 the sound of the voice is regulated. Of these there are 

 two pairs. The first, of which a portion is shewn in (Fig. 3 

 (a) and the whole displayed in Fig. 4 {a, a), extend from 

 the upper portion of the cricoid cartilage (Fig. 2, a) along 

 the two branches of the arytenoid cartilages (Fig. 2, h) in 

 the outer edge of each of which they are respectively 

 inserted, and serve to close the orifice. The second, 

 sufficiently visible in Fig. 3 {h, h), are those which open the 

 orifice, and arise from the lateral and posterior portion of 

 the cricoid cartilage (Fig. 2, a), and their fibres, passing- 

 over the closing muscles just described, are inserted on the 

 inner edge of each arytsenoid cartilage (Fig. 2, h). 



The tube of the windpipe, or trachea, is composed of two 

 membranes enclosing numerous rings forming a cylinder 

 from end to end. At first cartilaginous, they become bony 

 as the bird grows older, and their ossification begins in 

 front and gradually extends backward towards the gullet*. 

 So far then there is no essential difference between the 

 Raven and other birds in the parts described. 



The inferior larynx or syrinx, which is the real seat of 



* In certain birds ossification of all the tracheal rings is not completed. 

 Various inequalities of diameter and convolutions of the tube (some of which 

 will be hereafter described and figured) also occur, producing, as might be 

 expected, particular effects on the voice. Generally the proportionate length of 

 the trachea deserves consideration, for shrill notes are produced by short tubes 

 and vice versa. On the structure of the tube, too, certain effects depend. As a 

 general i-ule, though not without exceptions, birds which possess strong and 

 broad cartilages or bony rings have a raonotonons and loud voice, while slenderer 

 rings with wider interspaces allow a freedon) of motion producing a correspond- 

 ing variety in the .'icale of tone. 



