252 SPECIAL PHYSIOLOGY. 



oblongata, consist of three portions, which are all given off from the 

 gray matter within the posterior part of the medulla oblongata and 

 spinal cord. The first, called the glosso-pliaryngeal nerve, is the 

 smallest and highest; it passes out through the base of the skull into 

 the neck, and supplies chiefly, as its name implies, the mucous mem- 

 brane of the tongue, and the lining membrane, and partly the mus- 

 cles, of the pharynx; but it also sends branches to the tonsils, the 

 palate and its muscles, and the Eustachian tube, and even to the tym- 

 panum or middle ear. The second or largest portion of the eighth 

 pair, named the pneumogastric nerve, par vagum, or vagus nerve, 

 leaves the sides of the medulla oblongata, passes through the base of 

 the skull into the neck, and is distributed chiefly, as its first name in- 

 dicates, to the lungs and stomach. It is called vagus, or the wander- 

 ing nerve, from the great distance from the head, to which its branches 

 extend. Besides the stomach and lungs, it moreover supplies branches 

 to the muscles and lining membrane of the pharynx, to the lining 

 membrane and muscles of the larynx, the lining membrane and mus- 

 cular fibres of the windpipe, the mucous and muscular coats of the oeso- 

 phagus, and, lastly, a most important portion of the nerve, cardiac 

 branches, which go to the heart. The third division of the eighth pair, 

 named the spinal accessory nerve, arises, by many funiculi, from the 

 lateral columns of the spinal cord, low down in the neck, and therefore, 

 from its origin, might be deemed a spinal nerve ; but it ascends through 

 the foramen magnum into the skull, receives additional roots from the 

 sides of the medulla oblongata, and then passes out through the base 

 of the skull, into the neck ; here it communicates with the pneumo- 

 gastric nerve, and then descends obliquely downwards, and supplies 

 chiefly the sterno-mastoid, and trapezius muscles. The glosso-pharyn- 

 geal and pneumogastric nerves, have each ganglionic masses upon their 

 trunks; the spinal accessory nerve has no such ganglion. The ninth 

 pair of cranial nerves, 9, or hypo-glossal nerves, emerge from the front 

 of the medulla oblongata, between the olivary body and the anterior 

 pyramid, though their fibres arise deeply from gray matter at the back 

 part of the medulla. The nerves pass forwards, out of the cranium, 

 through special foramina in the occipital bone, and, entering the neck, 

 run onwards, to be distributed chiefly to the muscles of the tongue. 

 They also supply, however, most of the muscles in front of the neck. 

 In some mammalia, this nerve has a small posterior sensory root, hav- 

 ing a ganglion upon it, thus manifesting an affinity with the spinal 

 nerves, next in succession to it, which we have immediately to de- 

 scribe. 



Estimates have been made of the number of nerve fibres present in 

 several of the cranial nerves. The numbers in the following nerves, 

 which, as we shall hereafter see, are motor in function, are as follows : 

 the third or oculo-motor, 15,000; the fourth or pathetic, 1100; the 

 small root of the fifth, 9000 to 10,000; the sixth or abducent nerve, 

 2000 to 2500; the portio dura or facial, 4000 to 4500; the spinal ac- 

 cessory, 2000 to 2500; and the ninth or hypo-glossal, 4500 to 5000. 

 Of the other nerves, the glosso-pharyngeal is said to contain 3500, and 

 the pneumogastric 4000 small and 5000 larger nerve-fibres. 



