83 



the back or dorsal vertebrae, as the central S ; the 

 loins, or lumbar vertahra^ and sacrum, as the S for 

 moving tlie hinder limbs, or appiiis proper of the 

 trunk ; the neck as the S of combination ; and the 

 arms as the appnis of combination. 



We shall name these three S S S, beginning at 

 the head, iliejirst S, second S, and third JS ; or, the 

 7iecJc S ; the central, and from its more simple ac- 

 tion, the opjhidian'^' !S ; and the loin S. 



The relative actions of these three S S S be- 

 come quite changed from those of three successive 

 S S S in the snake, as will be explained. 



§ 84. The cavity formed by the ribs and the 

 breast-bone is filled by the lungs, and from the 

 extremities of the breast-bone go muscular cords 

 of connection to the head and to the pelvis. 



These cords of connection join the actions of the 

 central or opliidian S, with those of the loin S, 

 and the actions' of both these with those of the 

 neck S. 



The trunk, composed of the dorsal and lumbar 

 vertebrae, the ribs and sternum and the pelvis, may 

 be regarded as an S, of which the hinder limbs are 

 the ribs. We shall call this the composite S, The 



* Acting through the ribs, directly on its artificial ground, it has a 

 true opliidian or snake action. 



