TONS VAROLII. 117 



sure. Galvanic stimulation of the divided surface of the cord is followed 

 by a contraction of the blood vessels and a rise in the blood pressure. 



9. A Diabetic centre, irritation of which causes an increase in the 

 amount of urine secreted, and the appearance of a considerable quantity of 

 sugar. 



10. Respiratory centre, situated near the origin of the pneumogastric 

 nerves, presides over the movements of respiration and its modifications, 

 laughing, sighing, sobbing, sneezing, etc. It may be excited reflexly by 

 the presence of carbonic acid in the lungs irritating the terminal pneumo- 

 gastric filaments ; or automatically, according to the character of the blood 

 circulating through it ; an excess of carbonic acid or a diminution of oxygen 

 increasing the number of respiratory movements ; a reverse condition di- 

 minishing the respiratory movements. 



11. A Spasm centre, stimulation of which gives rise to convulsive phe- 

 nomena, such as coughing, sneezing, etc. 



12. A centre for certain ocular functions, governing the closure of the 

 eyelids and dilatation of the pupil. 



13. A Sweat centre is also localized in the medulla. 



NERVOUS CIRCLE OF RESPIRATION (ENTIRELY REFLEX). 



-p . f Pulmonary branches of the pneumogastric. 



Superior laryngeal. 



Centripetal \ Trifacia1 ' or 5th pair. 



jx v I Nerves of general sensibility. 



[ Sympathetic nerve. 



j, [ Phrenic, distributed to the diaphragm. 



| Intercostals, distributed to the intercostal muscles. 

 p t -f i ~\ Facial nerve, or portio dura, to the facial muscles. 



en n uga External branch of spinal accessory, to the trapezius 



erves " and sterno-cleido-mastoid muscles. 



PONS VAROLII. 



The Pons Varolii unites together the cerebrum above, the cerebellum 

 behind, and the medulla oblongata below. It consists of transverse and 

 longitudinal fibres, amidst which are irregularly scattered collections of gray 

 or vesicular nervous matter. 



The transverse fibres unite the two lateral halves of the cerebellum. 



The longitudinal fibres are continuous (i) with the anterior pyramids of 

 the medulla oblongata, which interlacing with the deep layers of the 

 transverse fibres, ascend to the crura cerebri, forming their superficial or 

 fasciculated portions ; (2) with fibres derived from the olivary fasciculus, 



