LATERAL PART OF MIDDLE CRANIAL FOSSA 329 



The Ganglion Semilunare (O.T. Gasserian) is somewhat 

 crescentic in form. It lies upon the sutural junction between 

 the apex of the petrous bone and the great wing of the 

 sphenoid bone, where it is enclosed within a recess or space, 

 called the cavum Meckelii^ formed by a separation of the two 

 layers of the dura mater. The concavity of the ganglion is 

 directed postero-medially, and it is upon this aspect that it 

 receives the interlacing fibres of the sensory root of the 

 trigeminal nerve ; the convexity of the ganglion is directed 

 antero-laterally and from it emerge the three main divisions 

 of the trigeminal nerve. These 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 portio minor or motor root of the fifth nerve should now 

 be followed. Before the nerve pierces the dura mater the 

 motor root lies along the medial side of the large sensory root, 

 but it soon changes its position and comes to lie beneath 

 the sensory part. To display this relationship, draw the 

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

 mater which leads into the cavum Meckelii, and, gently 

 dislodging the semilunar ganglion from its place, turn it 

 antero-laterally so as to expose its deep surface. The small 

 and firm motor root can readily be recognised lying in a 

 groove upon the deep surface of the ganglion ; and if it is 

 displaced from this, 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. This junction may take place within the 

 cranium, in the foramen ovale, or immediately outside the 

 skull. 



The three principal divisions of the trigeminal nerve may 

 next be examined. Begin with the mandibular division, 

 which is the largest. This proceeds directly downwards, and 

 almost immediately leaves the cranial cavity through the 

 foramen ovale. 



-- Whilst isolating this large nerve -trunk 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 this 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. 



