968 THE NERVOUS SYSTEM 



orbital nerves, namely, the posterior superior alveolar branches, the middle superior 

 alveolar branch, and the anterior superior alveolar branches. 



The posterior superior alveolar (dental) nerves are usually two in number, but 

 sometimes arise by a single trunk. They pass downwards and outwards through the 

 pterygo-maxillary fissure into the zygomatic fossa, where they give branches to the 

 mucous membrane of the gums and the posterior part of the mouth ; then they enter 

 the posterior alveolar (dental) canals and unite with the other alveolar branches to 

 form the superior dental plexus, through which they give branches to the roots of the 

 molar teeth and to the mucous membrane of the maxillary sinus (fig. 702). 



(c) The branches given off in the infra-orbital sulcus and canal are the middle and 

 anterior superior alveolar (dental) nerves. 



The middle superior alveolar (dental) nerve leaves the infra-orbital nerve in 

 the posterior part of the infra-orbital sulcus, and, passing downwards and forwards 

 in a canal in the maxilla, it divides into terminal branches that anastomose with the 

 other alveolar branches to form the superior dental plexus. Through the plexus it 

 supplies the bicuspid teeth and gives branches to the mucous membrane of the 

 maxillary sinus and also to the gums (fig. 702). 



The anterior superior alveolar (dental) nerve is the largest of the superior 

 alveolar nerves. It is given off by the infra-orbital nerve in the anterior part of the 

 infra-orbital canal, and passes downwards in a bony canal in the anterior wall of the 

 maxilla. After uniting with the other alveolar nerves to form the superior dental 

 plexus, it supplies the canines and the incisors and gives branches to the mucous 

 membrane of the maxillary sinus and the gums (fig. 702). It also gives off a nasal 

 branch which enters the nasal fossa through a small foramen, and supplies the 

 mucous membrane of the anterior part of the inferior meatus and the adjacent part 

 of the floor of the nose. 



The superior dental plexus is formed in the bony alveolar canals by the three 

 superior alveolar nerves. It is convex downwards and anastomoses across the mid- 

 line with the corresponding plexus of the other side (fig. 702) From it arise the 

 superior dental branches supplying the roots of the teeth, superior gingival 

 branches supplying the gums, and also branches to the mucous membrane of the 

 maxillary sinus and to the bone. On the plexus are two gangliform enlargements, 

 one, called the ganglion of Valentine, situated at the junction of the middle and the 

 posterior branches, and the other, called the ganglion of Bochdalek, at the junction of 

 the middle and anterior branches. 



The infra-orbital nerve, that part of the maxillary nerve lying distal to the 

 spheno-palatine ganglion, enters the orbit through the inferior orbital (spheno- 

 maxillary) fissure, accompanied by the infra-orbital artery, and with it passes through 

 the infra-orbital canal (fig. 702) to the face, where it divides into four sets of terminal 

 branches, some of which, by anastomoses with the branches of the facial nerve, form 

 the infra-orbital plexus. 



(d) The terminal branches of the maxillary nerve are the inferior palpebral, the 

 external and internal nasal (nasal), and the superior labial. 



The inferior palpebral branches, usually two, pass upwards and supply all 

 the skin and conjunctiva of the lower eyelid (fig. 705) . 



The external nasal branches pass inwards under cover of the quadratus (levator) 

 labii superioris, and supply the skin of the posterior part of the lateral aspect of the 

 nose. 



The internal nasal branches pass downwards and inwards under the lateral 

 wall of the nose, and then turn upwards to supply the skin of the vestibule of the nose. 



The superior labial branches, three or four in number, as a rule are larger than 

 the palpebral and nasal branches. They pass downwards to supply the skin and 

 mucous membrane of the upper lip and the neighbouring part of the cheek. 



THE MANDIBULAR NERVE OR THIRD DIVISION OF THE TRIGEMINUS 



The mandibular division is the largest of the three divisions of the fifth nerve 

 (figs. 703 and 705). It is formed by the union of two distinct parts, namely, the en- 

 tire motor root of the fifth nerve and a large bundle of sensory fibres derived from the 

 semilunar (Gasserian) ganglion. These two parts pass through the foramen ovale 

 and unite immediately outside the skull to form a large trunk which almost 

 directly after its formation divides into a small anterior and a larger posterior por- 



