344 VETERINARY LECTURES 



562. The Medulla Oblongata (Plate XXXV III., A 3, B 3).— 

 The connective medium between the brain and the spinal cord con- 

 sists of white and grey nerve matter, but differs from the brain 

 proper in having the grey matter internally. Its functions are of 

 vast importance to life, as it regulates and controls the actions of 

 breathing, swallowing, etc. 



563. The Spinal Cord (Plate XX XVI I., D, and Plate XX XVI 1 1., 

 C 1 to 8) is a long irregular, cylindrical mass of nerve matter running 

 through the vertebral column. It is composed of white matter 

 externally, the centre being grey, and, like the brain, it is covered 

 with three similar membranes. As it passes along the vertebral 

 canal nerves are given off in pairs, and pass out between each 

 vertebral section. The upper root of these nerves is sensory, con- 

 veying sensation from the part of the body to which it is distributed 

 to the brain. The lower root of these pairs, on the other hand, conveys 

 motor power from the brain to the muscles, etc., that are supplied by 

 it, these being more or less under the control of the will. 



564. The Cranial Nerves, or nerves given off from the brain 

 direct, are arranged in pairs, twelve in number : 



1st pair. — The olfactory, which go to the nose, and give the 

 special sense of smell. 



2nd pair. — The optic, which go to the eyes, and give the 

 special sense of sight. 



3rd pair. — The motores oculorum, which supply the muscles of 

 the eyeballs (with two exceptions) with motor power. 



4th pair. — The pathetic, which supply one muscle of each 

 eyeball with motor pow r er. 



5th pair. — The trifacial, which are mixed (sensory and motor) 

 nerves, and supply the different parts of the face, 

 tongue, etc. 



6th pair. — The abducens, which supply one muscle of each 

 eyeball with motion. 



