634 THE VALVULAR ACTION OF THE LAKYNX. 



when they are touching by their summits. It results from this, 

 tliat by the approximation of the true cords the glottis is not 

 closed, and that there remains always a passage for the air 

 behind the membranous part. Mr. Mandl thinks that this is 

 peculiar to the species which run rapidly.) 



In the Howling Ape* {Mycetes) the hyoid is enormously de- 

 veloped in the form of a bell to lodge the air sacs peculiar to 

 this animal. There are also air sacs in the pharynx. 



In Simia sahceali at the root of the epiglottis, and above the 

 ligaments, there is a transverse opening which leads to a mem- 

 branous sac situated between the thyroid cartilage and the 

 hyoid bone. In the walls of the sac the fibres are partly tendi- 

 nous and partly muscular. 



In Simia jparniscoX there is a sac between the cricoid and 

 trachea. The trachea has continuous rings in some Simians. 



If the view that the function of the false cords or ven- 

 tricular bands is to close the glottis during effort, and tlius to 

 £x the thorax, we should expect them to be very strongly 

 developed in those animals whose habits render such fixation 

 likely to be serviceable ; on the other hand, we should expect 

 them to be absent in those animals where fixation of the thorax 

 would be of little or no service ; and this seems to be actually 

 the case. 



In animals whose motions are chiefly those of running, we 

 find the ventricular bands absent, or slightly developed. But 

 in animals where the anterior extremities are used for striking, 

 hugging, or climbing, the vocal cords are strongly developed. 

 We might at first expect also, that in cases where the anterior 

 extremities were employed for the purpose of prehension, we 

 would also find the ventricular bands developed. But this is 

 not always the case. 



When engaged in any very delicate work where the least 

 oscillation of the hand might be injurious, we often hold our 

 breath, but for ordinary prehensile actions we do not close the 

 glottis, unless considerable effort is required at the same time. 

 In marsupials such as the kangaroo, the anterior extremities 



• Op. cit., p. 448, t Ihid.y p. 1. 



t Wolff, p. 1. 



