THE HEAD AND NECK 1217 



formed alternately on each side the lateral oblique movements, as in grinding 

 or chewing, take place, and the condyle and iibro-cartilage of one side move 

 forwards and backwards, whilst the other condyle and fibro-cartilage move 

 in the opposite direction. During these movements oblique rotation is taking 

 place in the lower compartment of the joint. 



Muscles Concerned in the Movements. — Depression is effected by the 

 platysma myoides, mylo-hyoid, anterior belly of the digastric, and genio- 

 hyoid muscles ; and elevation by the anterior fibres of the temporal, masseter, 

 and internal pterygoid muscles. Protraction is produced by the external 

 pterygoid, the superficial fibres of the masseter, and slightly by the internal 

 pterygoid ; and retraction by the posterior fibres of the temporal, and the 

 deep fibres of the masseter. The grinding movement is effected by the external 

 pterygoid muscles acting alternately. 



The Superior Maxillary Nerve. 



The superior maxillary nerv'e is the second division of the fifth 

 cranial nerve, and in size is intermediate between the inferior maxil- 

 lary and the ophthalmic. It is entirely sensory, and arises from 

 the Gasserian ganglion. Its course is forwards to the foramen 

 rotundum, by which it leaves the cranial cavity. Thereafter it 

 enters the posterior part of the spheno -maxillary fossa, and then 

 crosses the upper part of that fossa to the spheno-maxillary 

 fissure, through which it passes on to the floor of the orbit. It now 

 takes on the name of the infra-orbital nerve, and traverses the 

 infra-orbital groove, and then the infra-orbital canal, on the floor 

 of the orbit. Finally, it emerges from this canal through the infra- 

 orbital foramen, under cover of the levator labii superioris, and ends 

 in its terminal branches. The course of the superior maxillary 

 nerve (and its continuation under the name of the infra-orbital 

 ner\^e) is almost directly forwards, there being a slight inclination 

 outwards. 



Branches. — ^These are as follows : 



Intracranial. In Infra-orbital Canal. 



Recurrent meningeal. Middle superior dental. 



Anterior superior dental. 



In Spheno-maxillary Fossa. Facial. 



Orbital or temporo-malar. Inferior palpebral. 



Spheno-palatine. Lateral nasal. 



Posterior superior dental. Superior labial. 



The recurrent meningeal branch supplies the dura mater of the 

 middle cranial fossa. 



The orbital or temporo-malar nerve is the first branch of the 

 superior maxillary in the spheno-maxillary fossa. It arises from its 

 upper surface, and enters the orbit through the spheno-maxillary 

 fissure. For its further course, see p. 1082. 



The spheno-palatine nerves are two in number. They arise from 

 the lower aspect of the parent trunk, and, after a very short de- 

 scending course, they end for the most part in Meckel's ganglion, 

 to which they convey sensory fibres, and of which they are the 



77 



