VERTEBRATED TYPE OF STRUCTURE. 85 



" bi-lateral symmetry " extends to the arrangement of those 

 internal parts which are connected with the functions of 

 animal life ; namely, the nervous system, the organs of sense, 

 and the muscular apparatus. But it does not always extend 

 to the organs of nutrition, which are unequally disposed on 

 the two sides : thus, in Man, the heart and stomach are on the 

 left side, and the liver on the right, while the lungs are much 

 larger on the right side than on the left. But in many of the 

 lower Vertebrata, there is an almost perfect symmetry in the 

 disposition of these organs, as there is also in the early embryo 

 of those in which this symmetry is subsequently departed 

 from ; so that it may be truly said that this symmetry is cha- 

 racteristic of the Vertebrate type, although for special purposes 

 it is frequently superseded. 



Fig. 25. SKELETON op THE OSTRICH. 



71. In all Vertebrated animals, the skeleton is chiefly 

 internal (fig. 25); and consists of bones, which are capable of 



