LUNGS OF THE ROOK. 27 



to draw the inferior larynx downwards, or to prevent it from 

 being pulled too far upwards by the action of the contractor 

 tracheas, s s ; or to aid the action of that muscle in shortening 

 the trachea. Here it is a distinct muscle, but in many birds 

 it forms a direct continuation of the contractor tracheae, s s. 



We have thus traced eleven pairs of muscles belonging to the 

 trachea : five pairs being appropriated to the larynx, two pairs 

 to the tube of the trachea, and four pairs to the syrinx, or in- 

 ferior larynx. You will find the number stated in books to be 

 much less ; but we take our lessons from nature, and regard 

 no other authority. It is by these muscles that the different 

 parts of the air-tube are stretched and relaxed, opened and 

 closed, so as to produce modulated sounds ; and all this com- 

 plex apparatus is necessary to enable a Rook to emit its various 

 cries, which, however, are much more numerous than is gene- 

 rally supposed, and fully as diversified as those of the Black- 

 bird, although it has not the faculty of emitting them in con- 

 tinuance, so as to form what is called a song. 



The part which seems to be analogous to the vocal cords in 

 man, is a dense, whitish elastic ligament extended between the 

 extremities of the last half ring of the trachea on each side, at 

 b b. Fig. 15, but which will be better seen in another figure. 



The lungs. Fig. 1, t t, are two oblong, depressed, spongy, 

 but rather dense bodies, situated in the upper part of the thorax, 

 extending from the first to the sixth rib, 1, 6, presenting be- 

 neath or towards the sternum a flattish surface, and being 

 above transversely and deeply grooved by the ribs. Inferiorly, 

 they are covered, supported and confined by a membrano-ten- 

 dinous expansion analogous to the diaphragm in quadrupeds, 

 and into which are inserted some slender muscular slips, « v v>, 

 coming from the hind ribs. Being thus bound down, they re- 

 ceive little dilatation during inspiration, and their upper or 

 dorsal surface, instead of being free, as in the mammalia, is at- 

 tached to the pleura costalis by a very delicate cellular tissue. 

 Two of the bronchial apertures communicating with the tho- 

 racic cells are seen at u u. Behind the lungs are placed the 

 kidneys, on the inferior surface of the anterior lobes of which 

 are seen the testes. 



