392 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



the note or notes emitted by a bird ; but as yet we 

 have no definite information as to the meaning of 

 those convolutions of the trachea which are so com- 

 mon in swans and ducks, and sometimes give to 

 the tube the appearance of a French horn (Darwin). 

 In some grouse resonance is aided by the development 

 of air sacs which are capable of inflation ; the great 

 throat-pouch of the European bustard appears to 

 have a similar function. 



Among the Mammalia the larynx becomes re- 

 markably complicated, a number of special cartilages 

 being developed, which are connected together by 

 ligaments, and moved on one another by special mus- 

 cles ; the whole function of this apparatus is to alter 

 the form of the slit of the glottis, and to increase or 

 diminish the tension of the vocal cords. As this sub- 

 ject has been already dealt with in chap. xv. of the 

 " Elements of Human Physiology," we have here only 

 to point out that Mammals differ greatly in the sounds 

 that they make, the dog barking, the cat mewing, the 

 lion roaring, but that most agree in using the voice 

 more at the breeding season than at any other ; a few 

 mammals, such as the American Hesperomys cornutus, 

 and the gibbon (Hylobates), which, it is interesting 

 to observe, is one of the anthropoid or man-like apes, 

 may be distinctly said to sing. Man is remarkable 

 for his capacity for producing not only sounds, but 

 articulate speech, the wealth and extent of which is 

 much greater in the higher than in the lower races of 

 his species. 



In Fishes, sounds, when produced, are of course 

 but rarely associated with the passage into the air 

 bladder ; but Ceratodus has been observed to make 

 grunting noises, which are possibly involuntary. 

 Various Cyprinoid and Siluroid fishes are known to 

 make sounds, and in Callomystax, Haddon has dis- 

 covered that the agent by which they are produced 



