388 



PHYSIOLOGY 



CHAP. 



Particular mention should be made of the formatio reticularis 

 which occupies the entire central part of the bulb (Figs. 205 and 

 206) ; it consists of nerve-fibres that cross in every direction, and 

 form a network. The longitudinal bundles are intersected by the 

 transverse or arcuate fibres that traverse the raphe obliquely. 

 Between the fibres there is a considerable number of nerve-cells, 

 mostly of a large size. These, according to Deiters, send their 

 processes downwards, and their dendrites horizontally. The 

 formatio reticularis may be regarded as a special form of the 



ordinary grey matter 

 in which the cells are 

 irregularly scattered, 

 and form, as Kolliker 

 says, a diffuse nucleus. 

 It is probable that the 

 main functions of the 

 bulb depend on these 

 central multipolar ele- 

 ments of the formatio 

 reticularis (Ediuger) ; 

 the great physiological 

 significance of the bulb 

 also appears from the 

 fact that it contains the 

 nuclei of origin of most 

 of the efferent cerebral 

 nerves, as also the ter- 

 minal nuclei of most 

 of the afferent cerebral 

 nerves. The nuclei of 

 the hypoglossal, spinal 

 accessory, vagus, and 



(Sappey, 

 thre 



FIG. 207. The three pairs of cerebellar peduncles. 



after Hirschfield and Leveille.) On left side the three 

 cerebellar peduncles have been cut short ; on right side 

 the hemisphere has been cut obliquely to show its con- 

 nection with the superior and inferior peduncles. 1, 

 median groove of fourth ventricle ; 2, same groove at the 

 place where the auditory striae emerge from it to cross 

 the floor of the ventricle ; 3, inferior peduncle or restiform 

 body ; 4, funiculus gracilis ; 5, superior peduncle on 

 right side the dissection shows the superior and inferior 

 peduncles crossing each other as they pass into the white 

 centre of the cerebellum ; 6, fillet at side of the crura glOSSO - 

 cerebri; 7, lateral grooves of crura cerebri; 8, corpora -no-r^oa lio onHvalir wifh 

 quadrigemina. nElreiy Wll 



in the bulb; those of the 



acoustic, facial, and trigeminal nerves lie partly in it, partly in the 

 pons; those of the oculomotor and trochlear nerves are found 

 in the grey matter that surrounds the aqueduct of Sylvius in the 

 mid-brain. 



The origins of the motor, and terminations of the sensory, 

 nerves are, as we have seen, systematically arranged in the spinal 

 cord, so that they can be identified at a glance. In the medulla, 

 on the contrary, all segmental regularity is lost; the motor 

 and sensory elements here form irregular groups that make it 

 impossible from their relative positions to recognise their functions. 



Of the twelve pairs of cerebral nerves the 1st and 2nd, i.e. 

 the Olfactory and Optic nerves, are so different from the others in 



