234 



558. The Medulla Oblongata (Plate XXXV., A. 3., B. 3.)— the 

 connective medium between the brain and the spinal cord — consists 

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

 the grey matter internally. Its functions are of vast importance to 

 life, as it regulates and controls the actions of breathing, swallowing, 

 &c., &c. 



559. The Spinal Cord (Plate XXXIV., D. and Plate XXXV., 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 tipper root of these nerves is sensory, conveying sensation 

 from the part of the body to which it is distributed, to the brain. The 

 lower vcot of these pairs, on the other hand, conveys motor-power from 

 the brain to the muscles, &c., that are supplied by it, these being 

 more or less under the control of the will. 



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

 direct, are arranged in pairs, 12 in number: — 



ist pair. — The Olfactory, which go to the nose, and give the 



special sense of smell. 

 2nd pair. — The Optic, which go to the eye, 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 power. 



5th pair. — The Trifacial, which are mixed (sensory and 

 motor) nerves, and supply the different parts of the 

 face, tongue, &c. 



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

 eyeball with motion. 



