304 



INTERNAL ANATOMY OF HORSE. 



forms animal heat. It also exercises on the organs a stimulafc 

 ing action, without which the animal tissues cannot manifest 

 their true properties. The organs that carry out this ad of 

 respiration in mammalia are the lungs. They take in oxygen 

 from the surrounding air and pass out in return CO^. 

 organs of respiration, so essential to animal life, are 

 shut in, in the thoracic cavity, and are connected with the air 

 by, first, a cartilaginous tube (fig. 159, Tr) arising in the back 

 of the pharynx, and, secondly, by the tw<3 nasal cavities. These 

 latter open into the back of the mouth by two openings, the 

 so-called posterior nares, and to the air by the nostrils. 



The whole organs of respiration may be divided into foui 

 sections — (1) the nasal cavities; (2) the larynx; (3) trachea 

 and bronchi ; (4) the lungs. 



In the horse we shall notice verj' large nostrils : owing to the 



Fig. 159.— Median Luncitiidinal Section tiF Head and Uppee Part of 

 Nec.k of Horse. (Aftev Cliauve^tu.) 



A, Nasal seiitmii ; T, tongue, with hard palate above ; Sp, soft palate ; t's, frontal 

 liouo and snin.'^ ; Pn, posterior nares; Ep, epiglottis; C, cerebrum; Ch. cerebellum; 

 .s', occipital bone ; L, larynx ; Tr, trachea ; G, esophagus ; Sf>.C, si'iual chord ; C4 aud 

 Cv". atlas and axis. 



structure and size of tlie soft palate (fig. 159, Sp) at the back of 

 the mouth, the horse can only breathe through the nasal cavities, 



