116 HUMAN PHYSIOLOGY. 



motor stimuli exciting to action and coordinating the muscles of the palate, 

 pharynx and oesophagus, necessary for the swallowing of the food. The 

 secretion of saliva is also controlled by a centre in the medulla. 



NERVOUS CIRCLE OF DEGLUTITION. (2d and 3d Stages.) 



Excitor f Palatal branch of 5th pair. 



or j Pharnygeal branches of the glosso-pharyngeal. 



Centripetal 1 Superior laryngeal branches of the pneumogastric. 



Nerves. .[_ CEsophageal branches of the pneumogastric. 



Pharyngeal branches of the pneumogastric, derived 



Motor 



or 

 Centrifugal 



Nerves. 



from the spinal accessory. 

 Hypoglossal and branches of the cervical plexus. 

 Inferior or recurrent laryngeal. 

 Motor filaments of the 3d division of the 5th pair. 



Portio dura. 



4. A centre which coordinates the muscles concerned in the act of 

 vomiting. 



5. A^ Speech centre, coordinating the various muscles necessary for the 

 accomplishment of articulation through the hypoglossal, facial nerves and 

 the 2d division of the 5th pair. 



6. A centre for the harmonization of muscles concerned in expression, 

 reflecting its impulses through the facial nerve. 



7. A Cardiac centre, which exerts (i) an accelerating influence over the 

 heart's pulsations through accelerating nerve fibres emerging from the cer- 

 vical portion of the cord, entering the inferior cervical ganglion, and thence 

 passing to the heart ; (2) an inhibitory or retarding influence upon the 

 action of the heart, through fibres of the spinal accessory nerve running in 

 the trunk of the pneumogastric. 



8. A Vasomotor centre, which, by alternately contracting and dilating 

 the blood vessels through nerves distributed in their walls, regulates the 

 quantity of blood distributed to an organ or tissue, and thus influences 

 nutrition, secretion and calorification. The vasomotor centre is situated 

 in the medulla oblongata and pons Varolii, between the corpora quadri- 

 gemina and the calamus scriptorius. The vasomotor fibres having their 

 origin in this centre descend through the interior of the cord, emerge 

 through the anterior roots of spinal nerves, enter the ganglia of the sympa- 

 thetic, and thence pass to the walls of the blood vessels, and maintain the 

 arterial tomis\ they may be divided into two classes, viz. : vaso-dilators, 

 e. g., chorda tympani, and vaso-constrictors, e. g., sympathetic fibres. 



Division of the cord at the lower border of the medulla is followed by a 

 dilatation of the entire vascular system and a marked fall of the blood pres- 



