THE CRANIAL NERVES. 261 



objects are at a distance (long sight) ; (3) squint of the eye so 

 that it is directed outward and downward. 



Such a paralysis of the eye is sometimes accompanied by a 

 partial hemiplegia (see p. 271) of the opposite side of the body, 

 thus idicating that some destructive lesion (haemorrhage, de- 

 structive tumour) exists on one side of the midbrain, so that it- 

 involves the nucleus of origin of the third nerve and also the 

 pyramidal fibers lying near. Since the fibers of the third nerve 

 do not cross to the opposite side, but those of the pyramids do 

 (see p. 243), we get a crossed or alternating paralysis. Some- 

 times only one part of the third nerve may. be paralyzed, for 

 example, that portion going to the muscles of accommodation. 



THE FOURTH AND SIXTH NERVES. The fourth and sixth nerves 

 supply the two extra-ocular muscles not supplied by the third, 

 viz., the superior oblique (fourth) and the external rectus 

 (sixth), respectively. 



THE FIFTH NERVE. The fifth nerve is the largest, of the 

 cranial nerves, and is a representative mixed nerve. It supplies 

 the teeth. The motor branch runs to the muscles of mastica- 

 tion, the tensor muscle of the palate, the rnylohyoid muscle (in 

 the floor of the mouth) and the anterior belly of the digastric. 

 These last two mentioned muscles pull the hyoid bone and there- 

 fore the root of the tongue upward and forward during the act 

 of swallowing. Both mastication and swallowing are seriously 

 impaired when this nerve is paralyzed. The sensory fibers are 

 connected with the receptors for all the common sensations of 

 the head and face. As already explained, they are connected 

 witli the nerve cells of the Gasserian ganglion, which is lodged 

 in a depression near the apex of the petrous portion of the 

 temporal bone. Shortly after leaving this ganglion, the nerve 

 divides into three branches: (1) the upper or ophthalmic, carry- 

 ing the sensory nerve fibers for the conjunctiva, the mucous 

 membrane of the nasal fossae, and the skin of the eyebrow, fore- 

 head and nose. (2) Middle or superior maxillary, supplying 

 the meninges, the lower eyelid, the skin of the side of the nose 

 and upper lip and all the teeth and gums of the upper jaw. (3) 

 Inferior maxillary, supplying the teeth and gums of the lower 



