Page:The New International Encyclopædia 1st ed. v. 14.djvu/435

NERVOUS SYSTEM AND BRAIN. 385 NERVOUS SYSTEM AND BRAIN. rcspoiulin>j only to sensations or impressions of the moment, or varying' their listlessuess with ve-tk'ss and purposeless wanderings to and fro. Vhile not actually deprived of intelligence, they hail lost to all appearance the faculty of attentive and intelligent observation." THE RIGHT CEHEBB.IL BE.MI8PHKRE (HCMAN) SHOWING LO- CALIZABLE AREAS OS THE MEDIAN 8CUFACES. The separate localization of the diflferent emo- tions, such as hate, love, fear, etc., which the teachings of phrenology would lead one to expect, has never been accomplished. In fact, there is every reason to believe that no .such localization exists, the same parts of the cortex being con- cerned in very different emotions. The C'kani.l Nerves. The cranial or ence- phalic nerves arise from the under surface of the cncephalon or brain and leave the cranial cavity tlirough foramina in its floor. According to the older classification of Willis, the cranial nerves were divided into nine pairs. The later and now more generally used classification of Sommerring recognizes twelve pairs of cranial nerves. The names of these nerves, taken in order from before backward, are, according to these classifications, as follows: I Soraraerring I OUactory I Optic Motor oculi Pathetic Trifacial Abduceiia Facial (Hortio dura) Auditory (Portio mollis).. OloSBO-pharyngeal Piuniniop:astric Spinal accessory Hypoglossal Pair First Second Third Fourth Filth Sixth Seventh Eighth Ninth Tenth Eleventh Twelfth Willis Pair Fir.xt S.totkI Third Fnnrth Fifth Sixth Seventh '- Eighth } Ninth From the physiological standpoint these nerves fall into three" groups, according to their func- tions. (1) Motor nerves: (a) oculomotor; (b) pathetic; (c) abducens; (d) facial; (e) hy- poglossal. (2) Sensory nerves: (a) olfactory; {h) optic; (c) auditory. (3) Mixed nerves: (a) trifacial; (b) glosso-pharyngeal ; (c) pneumogas- tric; (d) spinal accessory. Of these the olfac- tory, optic, auditory, and parts of the glosso- pharyngeal and trifacial are sometimes classified by tliemsclves as nerves of special sense. " The cranial nerves are connected with the sur- face of the brain at various points. These points are known as the apparent or superficial origin of the nerves. From these points their fibres can be traced into the substance of the brain to their real or deep rtrigins in the gray matter. The cranial nerves, with the exception of the first (olfactory) and the second (optic), are analogous, both eiiibiyologically and anatomic- ally, to the spinal nerves. The motor root fibres of the cranial nerves are the axinies of neurones whose cell bodies are situated in the gray matter of the medulla and parts above (motor nuclei of the cranial nerves), just as the motor root fibres of the spinal nerves are the axones of neurones whose cell bodies are situated in the gray matter of the cord (anterior horns). These motor nuclei are the nuclei of origin for these nerves. They are nuclei of ter- mination for neurones of higher systems which serve to bring the periiiheral neurone under the control of higher centres. The neurones which constitute the sensory por- tions of the cranial nerves have their cell bodies situated in ganglia outside the central nervous ■system. These ganglia correspond to the pos- terior root ganglia of the spinal nerves. The outwardly directed processes of these cells pass to their periiiheral terminations, as do those of the spinal ganglia cells. The central axones of these neurones enter the medulla and form longi- tudinal tracts of fibres in a manner quite anal- ogous to the formation of tlie posterior columns by the central axones of the spinal ganglia cells. The sensory root fibres of the cranial nerves, however, do not ascend, as do those of the spinal nerves, but turn spineward, forming descending roots. These fibres terminate in the gray matter of the medulla (terminal nuclei of the cranial nerves) in the same manner as do the spinal sensory root fibres in the gray matter of the cord and medulla. The first, or olfactory nerve, is properly not a nerve, but a slender process of the brain which terminates in an enlargement, the olfactory bulb, from which the olfactory nerves themselves are given off. The size and development of this olfactory process and bulb vary greatly in differ- ent animals, being in man quite rudimentary as compared with animals noted for their acute sense of smell. The olfactory process is con- nected with the rest of the In-ain by three roots called respectively the internal, or sliort root, the middle, or gray "root, and the external, or long root. The olfi'ictory nerves proper, that is the bundles of filaments extending from the under surface of the olfactory bulb through the fora- mina in the cribriform plate of the ethmoid to the mucous membrane of the nose, are made up ot axones of neurones whose cell bodies are located in the nasal mucous membrane. In this respect the peripheral olfactory neurones differ from, all other human perijiluTal sensory neurones. Hie short, hair-like processes of these cells which pass outward toward the surface are the den- drites The centrally directed processes are the a.xones They are non-medullated, and, passing through the 'cribriform plate in bundles (olfac- tory nerves), enter the olfactory bulb, where they terminate in end-arborizations in the olfactory glomeruli. In the glomeruli they come into re- lation with the dendrites of the mitral cells of the olfactory lobe. The axones of these mitral cells are m'edullated and form the main mass of fibres which pass back to the brain tlirough the olfactory process or tract and its roots. The second cranial, or optic nerve, is the nerve concerned in the special sense of sight. It is distributed entirely to the eyeball. The nerves from the two eyes, passing backward and