CHAP. IL] THE BRAIN. 967 



FIG. 115. DIAGRAM TO ILLUSTRATE THE POSITION OF THE NUCLEI OF THE CRANIAL 

 NERVES. (Sherrington.) 



The brain is supposed to be viewed from the dorsal aspect, the cerebral hemispheres 

 and cerebellum having been cut away. The nuclei are represented as if seen 

 through transparent material. On the right side, the corpus striatum and 

 optic thalamus have been cut away horizontally to some little depth in order 

 to shew their internal structure. 



L. lateral, E. P. external posterior and J/. P. median posterior column of the 

 cord. I. P. inferior peduncle, S. P. superior peduncle, and P. middle peduncle 

 of the cerebellum, all cut across. The dotted curved lines, upper and lower, on 

 the right half of the figure to which the dotted line P.V. outside the figure 

 points, mark the upper and lower boundaries of the pons on the ventral aspect. 



The outline of the fourth ventricle is shewn by a bold thick line. In the floor of 

 the ventricle are shewn, on the right half : /p. fovea posterior. Th. trigonum 

 hypoglossi. T. ac. trigonum acusticum. e. t. eminentia teres. s. m. striae 

 medullares or acusticae. /. a. fovea anterior. I. c. locus caeruleus. I. g. 

 valve of Vieussens. 



Qp. posterior and Qa. anterior corpus quadrigeminum. Pg. pineal gland. Nr. 

 the outline of the red nucleus. 3, the third ventricle, in which C indicates 

 the middle or soft commissure. F. p. a. the pillars of the fornix, behind 

 which is indicated in the cavity of the third ventricle the hollow of the 

 infundibulum. C. C. g. the genu of the corpus callosum, between which and 

 the fornix the cavity often called the fifth ventricle is indicated. F. portion 

 of convolution of frontal hemisphere cut across. 



On the left side are shewn : C. S. corpus striatum. 0. T. optic thalamus. Pv. 

 pulvinar. T. a. Tuberculum anterius. ch. s. choroidal sulcus marking the 

 place of reflection of the choroidal plexus. On the right side are exposed : 

 NC. head of, Nc, end of tail of nucleus caudatus. dp', dp" the two parts 

 of the globus pallidus, and Pt, putamen of the nucleus lenticularis. N. a. 

 anterior nucleus. N. med. median nucleus, N. lat. lateral nucleus and Pv.' 

 pulvinar of the optic thalamus. Cia. front limb, Gig. knee or genu, dp. hind 

 limb of internal capsule. Ce. external capsule. Cl. claustrum. 



The numerals III. to XII. indicate the nuclei of the respective cranial nerves, all 

 shewn on the left side with the exception of the accessory-vago-glosso- 

 pharyngeal IX. X. XI., which to avoid confusion is placed on the right side. 

 V. is the motor nucleus of the fifth nerve with the descending root, V. a the 

 sensory nucleus of the same with the long ascending root. VIII. m. median 

 nucleus, VIII. /. lateral nucleus of the auditory nerve, n. a. nucleus ambiguus. 

 The ascending root of the ninth nerve is seen at the hind end of the combined 

 nucleus of IX. X. XI. 



impulses; but they may be fibres passing from the crus across 

 the raphe to the nucleus. This nerve has special relations with 

 the optic tract, but of these we shall speak when we come to 

 deal with the functions of the nerves. 



624. In attempting to understand the nature and relations 

 of these cranial nerves, it must be borne in mind that, while 

 morphological studies lead us to believe that, as the vertebrate 

 body has been developed out of an invertebrate ancestry, so the 

 brain of the vertebrate has arisen by a series of modifications 

 from the nervous structures placed at the head and around the 

 mouth of an invertebrate, the same studies teach us that such 

 an evolution has been accomplished by means of profound 

 changes. We have, for instance, reason to think that the 

 mouth of the vertebrate does not correspond to the mouth of 

 the invertebrate, but is a new structure, whose appearance has 



