THE KERVOUS SYSTEM. Ill 



crease or diminish the rapidity of respiratory movements. Thus involun- 

 tary respirations are induced by the sudden contact of cold with any part 

 of the skin, as in dashing cold water on 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 feeces, urine, or 

 foetus. 



(2.) Centre for Deglutition. 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 successive co-ordi- 

 nate and adapted movements necessary to the act of deglutition (p. 239, 

 Vol. I.). This is proved by the persistence of swallowing in some of the 

 lower animals after destruction of the cerebral hemispheres and cere- 

 bellum; its existence in anencephalous monsters; the power of swallowing 

 possessed by the marsupial embryo before the brain is developed; and by 

 the complete arrest of the power of swallowing when the medulla ob- 

 longata is injured in experiments. (3) A centre by which the move- 

 ments of mastication are regulated (p. 226, Vol. I.). (4) Through the 

 medulla oblongata, chiefly, are reflected the impressions which excite the 

 secretion of saliva (p. 232, Vol. I.). (5) Cardio-inliibitory centre for the 

 regulation of the action of the heart, through the pneumogastrics and 

 probably also, the accelerating fibres of the sympathetic (p. 127, Vol. I.). 

 (6) The chief vaso-motor centre. From this centre arise fibres which, 

 passing down the spinal cord, issue with the anterior roots of the spinal 

 nerves, and enter the ganglia and branches of the sympathetic system, by 

 which they are conducted to the blood-vessels (p. 154, Vol. I.). (7) Cilio- 

 spinal centre for the regulation of the iris, and other plain-fibred muscles 

 of the eye. (8 and 9) Centres or ganglia of the special senses of hearing 

 and taste. (10) The centre for speech, i.e., the centre by which the 

 various muscular movements concerned in speech are co-ordinated or har- 

 monized. (11) Centre by which the many muscles concerned in vomiting 

 are harmonized. (12) The so-called diabetic centre, or, in other words, 

 the grey matter in the medulla oblongata which, being irritated, causes 

 glycosuria (p. 283, Vol. I.), is probably the vaso-motor centre; and this 

 peculiar result of its stimulation is merely due to vaso-motor changes in 

 the liver. 



Though respiration and life continue while the medulla oblongata is 

 perfect and in connection with the respiratory nerves, yet, when all the 

 brain above it is removed, there is no more appearance of sensation, or 

 will, or of any mental act in the animal, the subject of the experiment, 

 than there is when only the spinal cord is left. The movements are all 

 involuntary and unfelt; and the medulla oblongata has, therefore, no 



