REFLEX CENTERS IN THE MEDULLA OBLONGATA. 749 



The center for coughing, according to Kohts, is situated above the 

 inspiratory center and is excited centripetally through the sensory 

 branches of the vagus. The centrifugal fibers are the expiratory nerves, 

 including the constrictors of the glottis. 



The phonation-center. The center for the control of the voice-mech- 

 anism is situated from the origin of the vagus upward to the quadri- 

 geminate bodies. New-born animals from which the brain was removed, 

 with preservation of this portion of the brain, are still able to cry. 



The center for the movements of sucking, as well as of chewing. The 

 centripetal nerves are the sensory fibers of the mouth, including those of 

 the lips (second and third divisions of the trigeminus and the glosso- 

 pharyngeal). The motor nerves for the movements of sucking are the 

 facial (the lips), the hypoglossal (the tongue), the third division of the 

 trigeminus (elevator of the lower jaw and the branches of the depressor 

 of the lower jaw). After transitory (by cocain) or permanent paralysis 

 of the trigeminus the sucking-reflex ceases. The same motor nerves take 

 part in the act of chewing, but the action especially of the hypoglossal 

 for the movement of the tongue and of the facial for that of the buc- 

 cinator is necessary to keep the food between the teeth. 



The center for the secretion of saliva is situated on the floor of the 

 fourth ventricle, and can be stimulated reflexly. Irritation of the 

 medulla oblongata, when the chorda tympani and the glossopharyngeal 

 nerve are preserved, causes active secretion of saliva; a lesser amount of 

 secretion when these nerves are divided; and, finally, none at all when 

 the cervical sympathetic also is destroyed. 



The center for the act of deglutition is situated on the floor ot the 

 fourth ventricle above the respiratory center and is stimulated through 

 the sensory nerves of the palate and the pharynx (second and third divi- 

 sions of the trigeminus and the vagus). The centrifugal path is through 

 the motor branches of the pharyngeal plexus. Irritation of the glosso- 

 pharyngeal does not cause swallowing, but rather inhibition of the act 

 of deglutition. On the other hand, every act of swallowing excited by 

 irritation of the palatine nerves or the superior laryngeal nerve causes 

 rapid, abortive contraction of the diaphragm (deglutitional breathing). 



The center for vomiting is discussed on p. 282. The relations be- 

 tween certain branches of the vagus and the act of vomiting have been 

 pointed out on p. 710. The center may be set into activity by direct 

 application of apomorphin or emetin. 



The upper center for the dilator muscle of the pupil and the unstriated 

 muscles of the orbit and the eyelids is situated in the medulla oblongata. 

 The pupillary fibers passing through the trigeminus arise from the origin 

 of this nerve and downward as far as the second cervical nerve (in 

 the rabbit). Anastomotic fibers pass from this point downward through 

 the lateral columns of the spinal cord to the ciliospinal region, and thence 

 through the three or four uppermost thoracic nerves into the cervical 

 sympathetic. The center is normally stimulated reflexly by cutting 

 off the light from the retina. It is irritated directly by states of the 

 blood causing dyspnea or by occlusion of the carotids. 



The center may be irritated reflexly also by stimulation of sensory 

 nerves of the trunk (sciatic). These fibers pass (from the sciatic) 

 through the two lateral columns up to the center. 



Finally, there is situated in the medulla a higher center, which 



