AND PHYSIOLOGY, 



279 



THE SOUNDS PRODUCED BY ANIMALS. 



492. Among vertebrates the production of vocal sounds is 

 confined to the air-breathing classes, since no fish or gilled 

 animal is able to make any sound by means of the special 

 organs which are provided for that purpose in other animals. 



493. Laryngeal Pouches, or Sacs. — Nearly every mam- 

 mal can make some vocal sound, and the structure of the 

 larynx in all very closely resembles that of man. The howl- 

 ing apes present the most striking difference in these organs. 

 They have pouches, or laryngeal sacs as they are called, 

 connected with the larynx, which increase the loudness of 

 the voice simply by the resonance of the voice in these cavities. 



494. The Two Larynges of Birds— The Trill of Birds. 

 — In birds the vocal organs are somewhat different from those 

 of man. There is in them a larynx, called the superior 

 larynx, at the summit of the trachea, which seems designed 

 mainly for the ingress and egress of air. But the vocal 

 sounds for which birds are so remarkable are made by what 

 is called the inferior larynx, which is situated at the lower 

 extremity of the trachea. This is most complex in birda 

 which have the greatest powers of song. The two or three 

 lower rings of the trachea are usually consolidated into one, 

 and in the interior a cross bone runs from front to back which 

 has upon its upper edge a small membrane of a crescentic- 

 shape, which is so lax that it can freely vibrate when the air 

 i3 made to pass rapidly over it. This in its action, is anal- 

 ogous to the reed of the clarionet or melodeon. It is by the 

 vibration of this membrane that the peculiar trill of many 

 singing-birds is so beautifully executed. The intensity of the 



492. What vertebrates alone can make vocal sounds? 493. What is said of the struc- 

 ture of the larynx in all mammals ? What is the peculiarity among the howling apes ? 

 494. How many larynges have hirds? Give the function of each. What peculiarity in 

 the lower part of the trachea ? 



