112 



as well as actual workers in giving the final turn 

 in discharging the old ones, two pair of small mus- 

 cles of very peculiar construction are especially 

 concerned. 



One pair of these, the Internal Oblique Muscles of 

 the Eyes, has been already described (§ 77), when 

 speaking of the snake. 



The other pair, the Digastrics, through which the 

 lungs are suspended by one end of each muscle 

 from the lower jaw, and, by the other end, from 

 the base of the skull, are, we believe, found only in 

 the higher animals. We shall describe them in con- 

 nection with the wind-pipe (§ 114), the action of 

 which, in the locomotion of the body, these muscles 

 may be said to express. 



§ 111. The Lungs, which may be described as an 

 " air sponge,'' but one absorbing from the interior 

 instead of the exterior surface, are enclosed in 

 cases which allow the air to enter and to leave 

 them by only one and the same opening. 



They are made up in man and the higher 

 animals, so far as our purposes are concerned, of 

 four"^ such inclosed portions, two on each side. 



The chest, as can easily be observed, has a coni- 



* There are, in fact, five such parts, three on the right side and two 

 on the left. This disposition may have reference to the heart, which is 

 on the left side. 



