828 THE NERVOUS SYSTEM 



prioceptive fibers for eye muscle tissue, (3) general visceral efferent fibers. 



The neuron bodies of the visceral efferent fibers are located in the Edinger- 

 Westphal nucleus of mesencephalon. The fibers from these neurons form the 

 preganglionic fibers which terminate in the ciliary ganglion. The postgan- 

 glionic fibers from cell bodies in ciliary ganglion innervate the intrinsic 

 (smooth) muscles of the ciliary body and iris. 



IV. Trochlear 



The fourth cranial nerve arises from neuroblasts in the posterior ventral 

 floor of the mesencephalon near the ventral commissure. The fibers grow 

 dorsad and somewhat posteriad within the wall of the mesencephalon to the 

 mid-dorsal line where they emerge to the outside and decussate (i.e. cross), 

 the nerve from one side passing laterad toward the eye of the opposite side 

 where it innervates the developing premuscle mass of the superior oblique 

 muscle (fig. 356A). 



Summary of functional components: ( 1 ) Somatic motor fibers controlling 

 superior oblique muscle, (2) general somatic afferent (sensory) fibers, i.e. 

 proprioceptive fibers from eye muscle tissue. 



V. Trigeminal 



The trigeminal nerve is a complex association of sensory and motor fibers 

 (fig. 356A, B). It has the following divisions: 



A. Ophthalmicus or Deep Profundus 



Composed of somatic sensory fibers to the snout region. Fibers originate 

 from neuroblasts in the dorso-anterior part of the neural crest cells which give 

 origin to the Gasserian (semilunar) ganglion. This portion of the semilunar 

 ganglion probably should be regarded as a separate and distinct ganglion. 

 One fiber from each bipolar neuroblast grows anteriad toward the snout while 

 the other fiber enters the wall of the metencephalon. These neurons later 

 become unipolar. 



Summary of functional components: General somatic afferent (sensory) 

 fibers. 



B. M axillaris 



The maxillary ramus of the fifth cranial nerve is composed of somatic 

 sensory fibers from the upper jaw and snout and mucous membranes in these 

 areas. The fibers arise from neuroblasts within the neural crest material which 

 forms the central mass of the semilunar ganglion. One fiber from each bipolar 

 neuroblast grows anteriad toward the snout while the other fiber grows mediad 

 to enter the wall of the metencephalon along with fibers from the ophthalmic 

 and mandibular divisions. These neurons later become unipolar. 



Summary of functional components: General somatic afferent (sensory) 

 fibers. 



