238 HEAD AND NECK 



antero-laterally and from it emerge the three main divisions 

 of the trigeminal nerve. They are (i) the first, or 

 ophthalmic division ; (2) the second, or maxillary division ; 

 and (3) the third, or mandibular division. The medial 

 border of the ganglion is connected with the internal carotid 

 sympathetic plexus by filaments of communication. 



The/0r//0 minor, or motor root, of the fifth nerve should now 

 be followed. Before the nerve passes into MeckePs cave the 

 motor root lies along the medial side of the large sensory 

 root, but it soon changes its position and then lies beneath 

 the sensory part. To display that relationship, draw the 

 cut ends of the two roots through the aperture in the dura 

 mater which leads into Meckel's cave, and, gently dislodging 

 the semilunar ganglion from its place, turn it forwards and 

 laterally so as to expose its deep surface. The small and 

 firm motor root can readily be recognised lying in a groove 

 on the deep surface of the ganglion ; if it is displaced 

 from the groove, it will be seen to have no connection with 

 the ganglion, but to be continued onwards towards the foramen 

 ovale. It ultimately joins the mandibular division of the 

 trigeminal nerve. The junction may take place within the 

 cranium, in the foramen ovale, or immediately outside the 

 skull. 



Dissection. The three principal divisions of the trigeminal 

 nerve may next be examined. Begin with the mandibular 

 division, which is the largest. It proceeds directly downwards, 

 and almost immediately leaves the cranial cavity through the 

 foramen ovale. 



Whilst isolating the mandibular division and defining the 

 bony aperture through which it makes its exit, look carefully 

 for the accessory meningeal artery, which enters the cranium 

 through the same foramen. If the injection has been forced 

 into the vessel it can easily be detected. An emissary vein 

 which connects the cavernous sinus with the pterygoid venous 

 plexus also passes through the foramen ovale. 



The maxillary division is composed entirely of sensory 

 fibres. It runs forwards, in relation to the lower and lateral 

 part of the cavernous sinus, and, after a short course within 

 the cranium, makes its exit through the foramen rotundum. 

 Near its origin it gives off a fine meningeal branch to the dura 

 mater of the middle fossa of the cranium. 



The ophthalmic division is the smallest of the three branches 

 of the trigeminal nerve, and, like the maxillary, it is com- 

 posed entirely of sensory fibres. It passes forwards, in the 



