ANATOMY OF A 17.8 MM. HUMAN EMBRYO 55 



N. trigeminus. The trigeminal nerve (plates 2, 3, 4 and 5) is 

 composed of sensory and motor components. The sensory fibers 

 arise from the large semilunar ganglion (G.s-L), which lies lateral 

 to the cavernous sinus {Sxav., plates 4 and 5), and form a large 

 trunk which enters the latero-ventral surface of the metencepha- 

 lon {Meten.) . The motor fibers issue from the metencephalon at 

 a point slightly ventro-cephalad of the sensory root. They form 

 a trunk of considerable size which crosses the medial surface of the 

 semilunar ganglion to join the mandibular nerve (plate 4). The 

 peripheral fibers leave the semilunar ganglion as three main 

 branches, the ophthalmic (N.oph.), the maxillary (iV.?nx.), and 

 the mandibular {N.vicL). 



The ophthalmic nerve passes to the orbit. Dorsal to the optic 

 stalk it gives a branch to both the oculomotor and trochlear" 

 nerves, then divides into naso-ciliary and frontal nerves. The 

 frontal (N.fr.) passes dorsal to the superior rectus and superior 

 oblique muscles, and breaks up into several branches of which 

 the supraorbital may be recognized by its dorsal direction. The 

 naso-ciliary (N.na.-cil.) passes ventral to these muscles, and can 

 be followed into the cephalic part of the corresponding lateral 

 nasal process. The maxillary nerve (Njnx.) soon after leaving 

 the semilunar ganglion becomes a bundle of loosely connected 

 fibers extending into the maxillary process ventral to the optic 

 vesicle (Ves.op.). 



The mandibular nerve {N.md.) receives, in addition to the sen- 

 sory fibers from the semilunar ganglion, the motor part of the 

 trigeminal nerve. It divides into a small cephalic and a large 

 caudal trunk. The former or buccal nerve at first extends 

 cephalad in company with the infra-orbital branch of the 

 stapedial artery {A.stp., pi. 2). Soon leaving this the buccal 

 nerve crosses the anlage of the parotid gland {GI.p.), and passing 

 cephalad, furnishes branches to the epithelium near the angle 

 of the rima oris. The larger, caudal trunk of the mandibular 

 as it crosses the tubo-tympanal ridge, divides into three branches;, 

 the auriculo-temporal, the inferior alveolar, and the lingual. The 

 latter near its origin is joined by the chorda tympani branch 

 (N.ch-ty7?ip., plate 3; ch.-ty., plate 2) of the facial nerve. 



