314 ANATOMY AND PHYSIOLOGY 



constitute the "vital knot." Consequently this part of the nerve 

 system presides over processes of the body which are necessary 

 to life itself, and when one remembers that the motor and sensory 

 fibers which connect the brain and cord all pass through the 

 medulla, it is easy to understand that injury here produces far- 

 reaching results. 



The pons varolii is associated with the medulla in its cranial 

 nerve connections; most of its fibers are conducting paths between 

 the other parts which lie in the cranial cavity. 



FIG. 202. THE AREAS AND CE.NTERS OF THE MESIAL ASPECT OF THE HUMAN 

 HEMICEREBRUM. (C. K. Milk.} 



The cranial nerves connect parts of the head and face, also 

 certain muscles of the neck, with the brain. Through the vagus 

 (or pneumogastric) nerve the heart, lungs and digestive organs 

 possess cranial connections. 



The vagus nerve and action of the heart. The nerve muscle 

 action of the heart is peculiar to itself both in structure and 

 function. The fibers of its tissue, or myocardium, are without 

 sarcolemma and entirely involuntary in action. Again, although 

 involuntary, they are striped] they are also short, broad and 

 branched to form a inuscle network just such a structure 

 as will insure vigorous action within a limited range of motion. 

 This action is probably to a large degree independent, since 



