47-i THE CRANIAL NERVES. 



may be secreted and the food be actually digested and disappear, 

 when introduced in small quantity. But when introduced in large 

 quantity, it remains undigested, and is found after death, with the 

 exterior of the mass softened and permeated by gastric juice, while 

 the central portions are unaltered, and do not even seem to have 

 come in contact with the digestive fluid. This is undoubtedly 

 owing both to the diminished sensibility of the mucous membrane 

 of the stomach, and to the paralysis of its muscular fibres. The 

 peristaltic action of the organ is very important in digestion, in 

 order to bring successive portions of the food in contact with its 

 mucous membrane, and to carry away such as are already softened 

 or as are not capable of being digested in the stomach. This 

 constant movement and agitation of the food is probably also one 

 great stimulus to the continued secretion of the gastric juice. The 

 digestive fluid will therefore be deficient in quantity after division 

 of the pneumogastric nerve, at the same time that the peristaltic 

 movements of the stomach are suspended. Under these circum- 

 stances, the secretion of gastric juice may be sufficient to permeate 

 and digest small quantities of food, while a larger mass may resist 

 its action, and remain undigested. The effect produced by division 

 of these nerves on the digestive, as on the respiratory organs, is 

 therefore of a complicated character, and results from the combined 

 action of several different causes, which influence and modify each 

 other. 



The effect produced upon the liver by section of the pneumo- 

 gastrics, as well as the influence usually exerted by these nerves 

 upon the hepatic functions, has been so little studied that nothing 

 definite has been ascertained in regard to it. We shall therefore 

 pass over this portion of the subject in silence. 



SPINAL ACCESSORY. This nerve originates, by many filaments, 

 from the side of the medulla oblongata, below the level of the 

 pneumogastric, and also from the lateral portions of the spinal cord, 

 between the anterior and posterior roots of the upper five or six 

 cervical nerves. These fibres of spinal origin pass upward, uniting 

 into a slender rounded filament, which enters the cavity of the 

 cranium by the foramen magnum, and is then joined by the fibres 

 which originate from the medulla oblongata. The spinal accessory 

 nerve, thus constituted, passes out from the cavity of the skull by 

 the posterior foramen lacerum, in company with the glosso-pharyn- 

 geal and pneumogastric nerves. Immediately afterward it divides 



