CRANIAL NERVES I91 



445. The spinal nerves are quite uniform in their rehitions 

 so far as described above, but the cranial nerves are consider- 

 ably modified. The olfactory (I) and optic (II) nerves are not 

 comparable with spinal nerves at all. The III, I\', and VI go 

 to the muscles of the eye ball and contain no receptor elements. 

 The VIII nerve is the auditory and is purely receptor. The 

 V and VII nerves supply the skin and muscles of the face and 

 lower jaw, and are mixed in function. The IX nerve sui)i)Hes 

 the muscles and sense organs of the tongue (taste) and j)harynx, 

 and is also mixed. The X nerve supplies the viscera from the 

 pharynx to the hver, including larynx, lungs, oesophagus and 

 stomach and heart. It is also a mixed nerve. The XI and 

 XII are chiefly effector in function; they supply chiefly muscles 

 of the neck region. 



ENERGY RELATIONS OF THE ANIMAL 



446. When an animal puts itself in motion, work is being 

 done, as is the case when any other body is being moved, and 

 when w^ork is being done there is an expenditure of energy. 

 However, throughout its life the animal is continually moving 

 itself as well as other bodies, and hence, as constantly expending 

 energy. And for a considerable portion of its life its capability 

 of expending energy increases, even though energy is constantly 

 being s-pent. Now, a fundamental postulate of j^hysics says 

 that energy is never created, but that wherever it a})pears it 

 has merely been transformed or transferred from some other 

 source. The animal may be exhausted temporarily and yet 

 after a while its power of expending energy is renewed. And 

 we know that the condition upon which this renewal of energy 

 depends is the supply of proper food to the organism. Thus 

 the food is apparently the energy source for the animal. 



447. If we analyze the foods of animals we fmd that the most 

 important by far, for their energy-yielding value, as food, are 



