THE NERVOUS SYSTEM 1487 



of the dorsal part of the pons Varolii, close to the inner side of the 



upper sensory nucleus, and beneath the floor of the upper or pontine 

 part of the fourth ventricle. The axons of the ceUs of this nucleus 

 form the larger part of the small motor root. The mesencephalic 

 or accessory nucleus is situated in the grey matter on the lateral 

 wall of the aqueduct of Syhnus. The fibres which arise from the 

 axons of the cells of this nucleus constitute the mesencephalic, 

 Sylvian, or descending motor fibres of the fifth nerve. They enter 

 the pons Varolii, and join the more numerous fibres from the pontine 

 or chief motor nucleus to form the motor root of the fifth nerve. As 

 the mesencephalic fibres descend they furnish many collaterals to the 

 pontine nucleus. 



The large sensory and small motor roots appear, close together, 

 on the lateral aspect of the ventral surface of the pons Varolii, the 

 motor root h'ing above, and slightly internal to the sensory root. 

 The sensory root enters, and the motor root emerges from, the pons 

 Varolii. 



Distribution. — ^The fifth cranial nerve has an extensive distribu- 

 tion through means of its three divisions — ophthalmic, superior 

 maxillary, and inferior maxillary. 



Ophthalmic Nerve (Sensory). — (i) The front part of the cranium; 

 (2) the integument of (a) the upper eyelid and [b) the root and tip 

 of the nose; (3) the anterior part of the nasal mucous membrane, 

 and the conjunctiva; (4) the eyeball; and (5) the lachninal gland. 



Maxillary or Superior Maxillary Nerve (Sensory). — (i) The integu- 

 ment of the malar and anterior part of the temporal regions; 

 (2) the integument of (a) the lower eyelid, {b) the side of the nose, 

 (c) the upper lip, and (i) the part of the face between the lower 

 eyelid and the upper lip ; (3) the pulps of the upper teeth, and the 

 mucous membrane of the upper gum ; (4) a large part of the nasal 

 mucous membrane ; (5) the mucous membrane of the maxillary- air- 

 sinus or antrum of Highmore ; (6) the mucous membrane of {a) the 

 naso-pharynx, and (6) the soft and hard palate and the tonsil. 



Mandibular or Inferior Maxillary Nerve (Sensory and Motor), — 

 The sensory distribution of this nerv^e is as follows: (i) The integu- 

 ment of (a) the temporal region, (&) the outer surface of the pinna, 

 and (c) the external auditory meatus; (2) the integument of the 

 lower lip, and that which covers the mandible; (3) the temporo- 

 mandibular joint; (4) the parotid salivary gland; (5) the mucous 

 membrane lining the buccinator muscle, and the integument cover- 

 ing that muscle (through means of the long or sensory buccal nerve) ; 

 (6) the mucous membrane (fungiform and conical papillae) of the 

 anterior two-thirds of the tongue (common sensation) ; (7) the sub- 

 maxillary and sublingual salivary glands ; and (S) the pulps of the 

 lower teeth, and the mucous membrane of the lower gum. 



The motor distribution of the inferior maxiUary ner\^e is as follows: 



(i) The muscles of mastication — namely, {a) the masseter, {b) the 



-temporal, and (c) the external and internal pterygoid muscles; 



(2) the mylo-hyoid muscle and anterior belly of the digastric ; (3) the 



