CRANIAL NERVES. s.'{ 1 



The trigeminus emerges from the pons by .two roots: a large 

 sensory root and a small motor root. The large root has the Gas- 

 serian, or semilunar, ganglion, while the small root runs beneath it. 

 From the semilunar ganglion emanate the ophthalmic, superior max- 

 illary, and a third branch, which joins the small root of the trifacial 

 to form the inferior maxillary nerve. The nasal branch of the 

 ophthalmic, ciliary, or lenticular ganglion gives off the ciliary nerves 

 for the ciliary muscle and iris. This ganglion receives motor fibers 

 from the oculomotor nerve and branches from the sympathetic. 

 The superior maxillary branch passes through the rotund foramen 

 of the sphenoid bone and gives off dental nerves and spheno-palatine 

 nerves which go to MeckeFs, or the spheno-palatine, ganglion. It 

 gives off nasal, palatine, and pterygoid nerves. The pter} r goid nerve 

 gives off a branch, the great petrosal, which enters the cranial cavity 

 through the cavity of the foramen lacerum and enters a canal on 

 the front of the petrous portion of the temporal bone to join the 

 facial nerve. The inferior maxillary nerve is formed of the small 

 motor root of the trigeminus and a third branch of the semilunar 

 ganglion, and makes its exit from the skull by the oval foramen. It 

 gives off the auriculo-temporal and the lingual nerve, which in its 

 course is joined by the chorda tympani of the facial and the inferior 

 dental nerves. On the sensory division of the inferior maxillary 

 nerve is seated the otic, or ganglion of Arnold. From it emanates 

 the small petrosal nerve, which enters the cranium through a fine 

 canal in the spinous process of the sphenoid bone and then courses 

 along a canal in front of the petrous portion of the temporal bone 

 to join the facial. The otic ganglion gives out filaments to the ten- 

 sor palati and tensor tympani muscles. 



Physiology. From the point of view of general sensibility the 

 trigeminus possesses a considerable domain. To it alone is intrusted 

 the giving of general" sensibility to nearly all parts which enter into 

 the composition of the head. In the external covering of the head 

 but one region escapes it. This is the lateral and posterior part of 

 the hairy scalp, the innervation for the latter coming from the cer- 

 vical nerves. 



As to mucous-membrane sensibility, trifacial innervation comes 

 only to the posterior third of the tongue, where the glosso-pharyn- 

 geal innervates the palate, with the middle and inferior parts of the 

 pharynx. 



These points being eliminated, it gives tactile sensibility not 



