DEVELOPMENT OF PERIPHERAL NERVOUS SYSTEM 825 



toward the source from whence the neuron receives its stimulation. That is, the dendrites 

 grow, and the neuron cell body as a whole moves, toward the particular nerve fiber 

 tract from which the impulses are received. As these impulses and fiber tracts vary 

 slightly with the particular environmental conditions under which the different animal 

 groups live, the location of the nuclei within the brain correspondingly will vary to a 

 degree within the respective vertebrate groups. It is- to be observed, also, that the nuclei 

 of origin of the afferent fibers of the cranial nerves, and of the cerebrospinal nerves in 

 general, are located outside of the central nerve tube, with the exception of the neuron 

 cell bodies of the second or optic nerve which are located in the retina, an extension of 

 the forebrain, and the mesencephalic nucleus of the fifth nerve. The nuclei of origin of 

 the efferent fibers are placed within the latero-basal areas of the nerve tube (fig. 3551).) 



(A) The nuclei of origin of the various motor components of the cranial nerves here 

 are shown to be located within fairly definite regions along the antero-posterior axis of 

 the vertebrate brain. Reference may be made to Fig. 3551, for the dorso-ventral distri- 

 bution of these nuclei. 



The following symbols are used: 



1. Somatic motor fibers are shown in solid black. 



2. Special visceral motor fibers are indicated in black with white circles. 



3. General visceral motor fibers are black with white markings. 

 Nuclei of origin within the brain are as follows: 



III — black = Edinger-Westphal nucleus, origin of general visceral efferent fibers of Oculo- 

 motor Nerve 

 III — cross lines = nucleus of origin of somatic motor fibers of Oculomotor Nerve 

 IV — cross lines = nucleus of origin of somatic motor fibers of Trochlear Nerve 



V — cross hatched = special visceral motor nucleus, origin of special visceral motor fibers 

 of Mandibular division of Trigeminal Nerve 



VI — cross lines = nucleus of origin of somatic motor fibers of Abducent Nerve 



VII — cross hatched = special visceral motor nucleus of Facial Nerve 



VII — black = superior salivatory nucleus (?), origin of general visceral motor fibers of 

 Facial Nerve 



IX — cross hatched = origin of special visceral motor fibers of Glossopharyngeal Nerve 

 (this nucleus represents the anterior portion of nucleus anthiguus of Vagus Nerve) 



IX — solid black = inferior salivatory nucleus (?), origin of general visceral motor fibers 

 of Glossopharyngeal Nerve 



X — cross hatched = nucleus ambiguus or origin of special visceral motor fibers of Vagus 

 Nerve 



X — solid black = dorsal motor nucleus, origin of general visceral motor fibers of Vagus 

 Nerve 



XI — cross hatched = probable nucleus of origin of special visceral motor fibers of Spinal 

 Accessory Nerve 



XII — cross lines = nucleus of origin of somatic motor fibers of Hypoglossal Nerve 



(B) Sensory nuclei or nuclei of termination of fifth, seventh, ninth, and tenth cranial 

 nerves, shown along thC' antero-posterior axis of the vertebrate brain. (The dorso-ventral 

 distribution of these nuclei is presented in Fig. 3551.) The nuclei of termination of the 

 eighth cranial nerve has been omitted. (Figs. A and B are schematized from data supplied 

 by Ranson, 1939, The Anatomy of the Nervous System. Philadelphia, Saunders.) 



(C) Cutaneous taste-bud branches of the right Facial Nerve in the fish, Anieiurus. 

 (Redrawn from Johnston, 1906, The Nervous System of Vertebrata, Philadelphia, Blakis- 

 ton, after Herrick.) 



(D) Head of the pollack, Pollachius virens. revealing seventh and tenth cranial nerve 

 distribution to lateral line system of the head. (Redrawn from Kingsley, 1912, Com- 

 parative Anatomy of Vertebrates, Philadelphia, Blakiston, after Cole.) 



