34 LABORATORY OUTLINE OF NEUROLOGY 



22. Complete the exposure of the brain, carefully preserving 

 the roots of the cranial nerves. 



Now, viewing the brain from above, review the arrangement 

 and physiological composition of the cranial nerves and note 

 particularly the part of the brain with which each peripheral 

 end-organ or group of physiologically similar organs is related. 

 Simple inspection shows that the organs of smell are connected 

 with the olfactory bulbs, and in fact these and almost the 

 whole of the cerebral hemispheres and epi thalamus and hypo- 

 thalamus form the olfactory part of the brain (stippled in Figs. 

 2 and 3) . In the same way the eyes are related with the optic 

 lobes of the midbrain (obliquely cross-hatched in Figs. 2 and 3), 

 the ears and lateral line organs with the acoustico-lateral area 

 (cross-hatched with horizontal lines), and the nerves of general 

 skin sensibility with the general cutaneous area (unshaded). 

 Locate precisely these areas on your specimen. 



23. Next carefully remove the membranous roof of the fourth 

 ventricle and study the floor of the fourth ventricle, noting the 

 following structures, passing from the median sulcus laterally 

 (cf. Figs. 2 and 6) : (1) a longitudinal ridge marking the position 

 of the fasciculus longitudinalis medialis ("posterior longitudinal 

 fasciculus") and farther ventrally the position of the ventral 

 gray column of the spinal cord and nuclei of the VI, IV, and III 

 cranial nerves — this is the somatic motor column; (2) a wide longi- 

 tudinal groove parallel with the last, below which are found the 

 motor nuclei of the X, IX, VII, and V cranial nerves — this is the 

 visceral motor column and is the forward extension of the lateral 



■ gray column of the spinal cord; (3) a longitudinal ridge with a 

 beaded contour, which contains the terminal centers of the 

 visceral sensory components of the X, IX, and VII cranial 

 nerves — the visceral sensory column; (4) separated from the last 

 by a deep groove and forming the dorso-lateral wall of the fourth 

 ventricle is the somatic sensory column. This column is the 

 continuation of the dorsal gray column of the spinal cord, and its 

 ventral part contains the centers for the general cutaneous nerves 

 of the trunk and head. The dorsal part of this column is the 

 area acustico-lateralis, whose anterior end is greatly enlarged 

 under the cerebellum, with which it is directly continuous. This 

 area receives the VIII and lateral line nerves, and the cerebel- 



