516 THE NERVOUS SYSTEM. 



The wide extent of connection which belongs to the 

 medulla oblongata as the centre of the respiratory move- 

 ments, is further shown by the fact that impressions by 

 mechanical and other ordinary stimuli, made on many 

 parts of the external or internal surface of the body, may 

 induce respiratory movements. Thus involuntary respira- 

 tions are induced by the sudden contact of cold with any 

 part of the skin, as in dashing cold water into the face. 

 Irritation of the mucous membrane of the nose produces 

 sneezing. Irritation in the pharynx, oesophagus, stomach, 

 or intestines, excites the concurrence of the respiratory 

 movements to produce vomiting. Violent irritation in the 

 rectum, bladder, or uterus, gives rise to a concurrent action 

 of the respiratory muscles, so as to effect the expulsion of 

 the faeces, urine, or foetus. 



The medulla oblongata appears to be the centre whence 

 are derived the motor impulses enabling the muscles of 

 the palate, pharynx, and oesophagus, to produce the suc- 



I cessive co-ordinate and adapted movements necessary to 

 the act of deglutition (see p. 263). This is proved by the 

 persistence of swallowing in some of the lower animals- 

 after destruction of the cerebral hemispheres and cerebel- 

 lum ; its existence in anencephalous monsters ; the power 

 of swallowing possessed by "marsupial embryoes before the 



' brain is developed ; and by the complete arrest of the 

 power of swallowing when the medulla oblongata is injured 

 in experiments. But the reflecting power herein exercised 

 by the medulla oblongata is of a much simpler and more 

 restricted kind than that exercised in respiration ; it is y 

 indeed, not more than a simple instance of reflex action by 

 a segment of the spinal axis, receiving impressions for this 

 purpose from only a few centripetal nerves, and reflecting 

 them to the motor nerves of the same organ. The incident 

 or centripetal nerves in this case are the branches of the 

 glossopharyngeal, and, in a subordinate degree, those of 

 the fifth nerve, seme of the branches of the sii erior laryn- 



