1232 



HUMAN ANATOMY. 



Optic 

 nerve 



of fibres from the chief motor nucleus. In its downward course the mesencephaHc root is 

 joined by numerous fibres which have their origin in the pigmented cells of the substantia ferru- 

 ginea (page 1081) of the same and, possibly, of the opposite side. 



The fibres from these various sources — the mesencephalic nucleus, the substan- 

 tia ferruginea and the motor nucleus — become consolidated into the motor root of 

 the trigeminal nerve, whose superficial origin (Fig. 1046) is just above that of the 

 sensory root, from which it is separated by some of the superficial transverse fibres 

 of the pons. Leaving the side of the pons, the motor root follows the same course 

 to and through the dura mater as does the sensory, to the inner side of.which it lies. 

 It eventually passes beneath the Gasserian ganglion to become exclusively an 

 integral portion of the mandibular division of the trigeminal. 



The cortical connections of the motor root are established by fibres that arise from cells 

 within the cortical gray matter of the lower third of the precentral convolution. Thence, as 

 constituents of the pyramidal tracts, they descend through the corona radiata, the internal cap- 

 sule and the cerebral peduncle into the pons, where, for the most part after decussation, they 

 terminate in end-arborizations around the radicular cells of tlie motor trigeminal nuclei. 



The Gasserian Ganglion.— The Gasserian ganglion (ganglion semilunare 

 [Gasseri]) (Fig. 1055) is an important complex of nerve-tibres and cells, which lies 



in a slight depression on the 

 Fig. 1055. apex of the petrous portion of 



the temporal bone. In shape 

 it is a flattened crescent with its 

 convexity forward, measuring 

 from 1.5-2 cm. in width and 

 about I cm. in length. The sur- 

 face of the ganglion presents an 

 irregular longitudinal or reticu- 

 lar striation. From the anterior 

 expanded convex border of the 

 ganglion arise the ophthalmic 

 and maxillary nerves and the 

 sensory portion of the mandib- 

 ular nerve, while its narrow 

 concave posterior margin is con- 

 tinued into the sensory root of 

 the fifth nerve. The ganglion 

 lies in Meckel's space (cavum 

 Meckelii), a cleft produced by a 

 delamination of the dura mater, 

 and comes in relation internally 

 with the cavernous sinus and 

 the internal carotid artery. Be- 

 neath, but unconnected with it, 

 are the motor root of the trifacial and the great superficial petrosal nerve. In struc- 

 ture it resembles a spinal ganglion, being composed of the characteristically modified 

 neurones, from whose single processes proceed the peripherally directed dendrites 

 and the centrally coursing axones. 



In addition to the three large trunks given off from the anterior margin, the 

 branches of the Gasserian ganglion include some fine meningeal filaments 

 which arise from the posterior end of the ganglion and are distributed to the adja- 

 cent dura mater. 



Ophthalmic 

 divisioi 

 V. nerve 



Gasserian 

 ganglion 



Gasserian ganglion of left side viewed from above; sensory and 

 motor roots and three divisions of trigeminal nerve are seen. 



Communications. — At its inner side the Gasserian ganglion receives filaments from the 

 adjacent carotid plexus of the sympathetic, which end in relation with the cells of the ganglion. 



Divisions of the Trigeminal Nerve. — These are three in number, the oph- 

 thalmic, the ma-xillary and the mandibular nerves. They arise from the anterior 



