726 



DISSECTION OF THE BRAIN. 



Parts iu 

 front of the 

 crura 

 cerebri. 



Olfactory 

 lobe. 



Definition. 



Origin is 

 apparent 

 and real. 



Real is from 

 grey matter. 



Classifica- 

 tion as 

 twelve pairs. 



Soemmer- 

 ing's. 



Designation 



from 



number, 



name of 

 part, 



or function. 



Olfactory 

 nerves. 



white bodies the corpora albicantia (e) ; and then a prominent 

 greyish mass, called tuber cinereum (li). From the tuber cinereum a 

 conical process, the infundibulum, descends to the pituitary body in 

 the sella Turcica of the sphenoid bone. 



Anterior to the tuber cinereum are the converging optic tracts ! 

 with their commissure (i). In front of the commissure lies a thin 

 greyish layer lamina cinerea (m) : and still farther forwards is the 

 great longitudinal fissure between the hemispheres, with the white 

 corpus callosum (n) in the bottom of it. 



At the inner end of the Sylvian fissure is a depression termed 

 the vallecula Sylvii (l\ at the bottom of which is seen another spot 

 perforated by vessels the anterior perforated space. 



Lastly, in front of the anterior perforated space, and resting on 

 the surface of the frontal lobe of the cerebral hemisphere, is the 

 elongated process of the brain (o) named the olfactory lobe, from which 

 the olfactory nerve-filaments spring. This process is frequently 

 called the olfactory nerve, but its true nature as a lobe of the 

 cerebrum is shown by its position and structure, as well as by its 

 condition in the lower animals, in which it is generally of large size. 



The CRANIAL NERVES take origin from the encephalon, with one 

 exception, the spinal accessory, and pass through apertures in the wall 

 of the cranium. 



The origin of a nerve is not determined by the place at which it 

 appears on the surface, for fibres or roots may be traced deeply into 

 the brain-substance. Each nerve has therefore a superficial or appa- 

 rent, and a deep or real origin. 



With respect to the superficial attachment there cannot be any 

 doubt ; but the deep origins, in consequence of the difficulty of tracing 

 the roots, are matters for the most part outside the possibilities of 

 ordinary dissection. "When the roots are followed into the encephalon, 

 they enter masses of grey substance, containing nerve-cells, which 

 are looked upon as nuclei of origin in the case of motor nerve fibres 

 or of termination in the case of sensory, or afferent, fibres. 



The cranial nerves are enumerated as forming twelve pairs. 

 According to this arrangement (Soemmering's) each trunk is con- 

 sidered a separate nerve, although it may be associated with others in 

 the foramen of exit. 



The several nerves may be designated first, second, third, and so 

 forth : this numerical mode of naming applies to all. 



But a second name has been derived for some of the nerves from 

 the parts to which they are supplied ; as instances of this nomen- 

 clature the terms pneumo-gastric. and hypoglossal may be taken. 

 A different appellation is given to others, in consequence of the 

 function conferred on the part to which they are distributed, as the 

 terms auditory, oculomotor and olfactory express. In this way two 

 names may be employed in referring to a nerve : one being 

 numerical, the other local or functional, as is exemplified below. 



The FIRST or OLFACTORY NERVES are about twenty fine filaments 

 which spring from the under surface of the olfactory bulb (fig. 260, x ) 



