Organs of Respiration and Circulation, 



591 



appearance in all animals, being slightly altered to suit the tones 

 uttered by each ; — this will be observed on comparing figs. 14 

 and 15, which represent the larynx of the horse and the ox. 



The larynx is composed of a number of cartilages which are 

 united to each other more or less firmly. One of these, the 

 epiglottis, a, figs. 14 and 15, defends the entrance into the wind- 

 pipe, and in the act of swallowing it rises and closes over the 

 opening of that tube, thereby preventing the. passage of the food 

 into it. Except in deglutition the epiglottis is always depressed 

 to preserve a free and open conduit for the air to and from the 

 lungs. The larynx is held in its situation through the medium 

 of a singularly shaped bone, the os hyoides, h, figs. 14 and 15, 

 which is united to the under and back part of the skull. The 

 OS hyoides gives attachment also to the muscles of the tongue, 

 and as this organ possesses a great freedom of action in ruminants, 

 we find the bone to be composed of more pieces in these animals 

 than in many others : these pieces are likewise connected to each 

 Fi^. 14. 



Fis. 15. 



The larynx of the horse. 

 a. The epiglottis, h. The os hyoides. 



The larynx of the ox. 



The references are the same as in 



Fi-. 14. 



Other by synovial joints. (Compare the os hyoides in the horse 

 and ox.) The necessity for a modification of the cartilages of the 

 larynx is apparent when we reflect on the varieties of the voice 

 of our domesticated animals. We recognise the horse by neigh- 

 ing, the ox by bellowing, the dog by barking, the sheep by 

 bleating, the pig by grunting, «Scc., &c. Many of these sounds 

 are influenced by the existence of folds in the lining membrane 

 of the larynx, called vocal cords. In the ox and the sheep we 

 have the simplest form of the organ, for bellowing and bleating 

 are little more than long-continued expiratory acts. 



