322 



THE VERTEBRATE BODY 



hindbrain. Five pairs of cranial nerves are attached to this region. 

 (These are: the trigeminal, which controls muscles of jaws, tongue, etc.; 

 the abducens, which also connects with a muscle of the eye; the facial, 

 which controls facial and ear movements and has to do with salivation 



BB 



Photos by Winchester 



Fig. 22.13. A complex reflex action in the frog. This frog has had the entire top of 

 his head cut off, thus removing all of the brain except the medulla. However, it is still 

 able to maintain a normal posture and, when stimulated with a needle, first raises itself 

 and then gives a powerful leap. With the cerebrum missing from the body this frog 

 could not have had any sensation of pain from the needle nor could the movement be 

 considered voluntary. The reaction, therefore, is explained only on the basis of reflex 

 action. These pictures were made with speed flash photography which gives^ an ex- 

 posure of only one five-thousandth of a second and thus "freezes"' the action. 



and tasting ; the auditory, which has to do with hearing and equilibrium ; 

 the glossopharyngeal, which is also concerned with salivation and tast- 

 ing; and the vagus, which sends branches down to the heart, lungs, 

 stomach, and intestine.) 



When the brain is dissected, it is found to contain four cavities 

 called ventricles which are connected to one another and with the canal 



