CONTENTS OF THE CHEST. 333 



increases the function of this sense, which sheep enjoy in 

 a very high degree. The nostrils at the upper and back 

 part terminate in a cartilaginous box called the larynx, which 

 is situated immediately beneath the pharynx or food-bag, so 

 that food, in passing into the latter, traverses the entrance of 

 the former, which, however, it is prevented from entering 

 by a triangular lid called the epiglottis : this lid in its usual 

 state is elevated from the glottis or entrance of the larynx, 

 so as to admit the free entrance and exit of the air, but the 

 passage of food forces it down so as to close the entrance 

 of the windpipe. The larynx is formed by four separate 

 cartilages besides the epiglottis just spoken of One is 

 shaped like a shield, and forms the front of the larynx and 

 great portion of its sides. Another below this is circular, 

 and two other smaller ones, shaped like an ewer, forms the 

 rims on which the epiglottis shuts down. The larynx is 

 lined throughout by a mucous membrane, which is endowed 

 with a high degree of sensibility, particularly at its upper 

 portion ; and thus when any foreign body accidentally en- 

 ters, or the mucus is in undue quantity, it excites the mem- 

 brane, and coughing is produced, by which it is expelled. 

 The idndpipe consists of a number of cartilaginous rings 

 connected together by elastic membrane so as to form a con- 

 tinuous tube passing down the front part of the neck, and 

 entering the chest between the two first ribs. The rings are 

 not completely cartilaginous, but the circle is made up of 

 membrane, the membranous part being on the upper portion 

 of the tube. This structure permits the windpipe to be bent 

 in any direction or compressed without injury, its elasticity 

 quickly restoring it to its former shape, or position. The 

 windpipe, on entering the chest, divides into two portions, 

 going to each division of the lungs ; and these subdivide into 

 others, which again ramify into numerous small tubes, which 

 ultimately terminate in very minute air-cells. The lungs, 

 which receive these terminations, form by far the greater 

 portion of the contents of the chest, which, however, it will 

 be proper to describe first. 



The chest of the sheep, in common with most quadrupeds, 

 is unlike that of the human body, becoming narrow towards 

 the lower part and terminating like the keel of a ship ; a 

 form more favorable to the flexion and extension of the fore- 

 legs, as well as of the shoulder-blades, than any other. 

 This keel-like form is, however, much less developed in the 



