A LABORATORY OUTLINE OF NEURO-ANATOMY 

 CRANIAL NERVE COMPONENTS OF THE DOGFISH 



357 



Somatic sensory. 



Somatic motor. 



Visceral sensory. 



Visceral motor. 



II. Optic 



III. Muscle sense 



IV. Muscle sense 



V. General cutaneous 

 VI. Muscle sense 

 VII. Lateral line fibers 



VIII. To the ear 

 IX. Lateral line fibers 



X. Lateral line and 

 general cutaneous 

 fibers 



III. To eye-muscles 



IV. To eye-muscles 

 VI. To eye-muscles 



I. Olfactory 



VII. General visceral 

 and gustatory 



IX, X. General visceral 

 and gustatory 



III. For intrinsic muscles 

 of the eye 



V. To the jaw muscles 



VII. To hyoid muscula- 

 ture 



IX, X. To branchial and 

 general visceral mus- 

 culature 



12. There are six pairs of cranial nerves associated with the medulla oblongata. The 

 tenth cranial or vagus nerve is one of the largest and arises by two series of roots. One 

 group of rootlets springs from the dorsolateral aspect of the medulla oblongata near its 

 lower end, and contains fibers which are distributed through the branchial and gastro- 

 intestinal rami of the vagus, while a large root, carrying fibers for the lateral line sense 

 organs, runs farther cephalad and enters the acusticolateral area. The ninth or glosso- 

 pharyngeal nerve, the nerve of the first branchial arch, arises from the medulla ob- 

 longata just ventral to this root of the vagus. Since the gills, as well as the gastro- 

 intestinal tract, are visceral organs, both the ninth and tenth nerves carry many visceral 

 fibers. The eighth or acoustic nerve arises from the side of the medulla opposite the 

 caudal part of the cerebellum in company with the fifth and seventh nerves, and ends 

 in the membranous labyrinth of the ear. Like the vagus, the facial or seventh cranial 

 nerve has, in addition to its main root, another, which runs further dorsally into the 

 acusticolateral area. This root carries sensory fibers for the lateral line organs of the 

 head. The sixth or abducens nerve arises more ventrally at the same level as the eighth^ 

 The fifth, or trigeminal nerve, which sends many branches to the skin of the head, is 

 represented by a large root emerging from the medulla oblongata in company with 

 the seventh. Some idea of the peripheral distribution of these nerves can be gained 

 from a study of Figs. 12 and 13. 



13. The floor of the fourth ventricle should now be exposed by carefully tearing away 

 the membranous roof of that cavity. The floor presents for examination a series of 

 longitudinal ridges and furrows which are of importance because they mark the position 

 of longitudianl columns (Figs. 8, 13), to each of which a special functon can be assigned. 

 A ridge on either side of the midline represents the position of the median longitudinal 

 bundle, beneath which lie the nuclei of the third, fourth, and sixth cranial nerves. 

 Since these nerves supply somatic musculature, the longitudinal elevation marks 

 the position of the somatic motor column. Separated from this ridge by a broad furrow 



