STRUCTURE OF THE MEDULLA OBLONGATA. 



.4.1 



the lateral surface of the bulb. Towards the upper end it passes near the pos- 

 terior margin of an oval prominence on the surface of the bulb termed the 

 olivary body or lower olive (0), but is separated from that prominence by a tract 

 of longitudinal fibres. In transverse sections of the lower part of the medulla 

 Fig. 32. VIEW PROM BEFORE OF THE 



MEDULLA OBLONGATA, PONS VAROLII, 

 CRURA CEREBRI, AND OTHER CENTRAL 

 PORTIONS OK THE ENCEPHALON. (Allen 



Thomson.) NATURAL SIZE. 



On the right side the convolutions of 

 the central lobe or island of Reil have 

 been left, together with a small part of 

 the anterior cerebral convolutions : on 

 the left side these have been removed by 

 an incision carried between the thalamus 

 opticus and the cerebral hemisphere. 



1', the olfactory tract cut short and 

 lying in its groove ; II, the left optic 

 nerve in front of the commissure ; II', 

 the right optic tract ; Th, the cut surface 

 of the left thalamus opticus ; C, the 

 central lobe or island of Reil ; Sy, fissure 

 of Sylvius ; x x , anterior perforated 

 space ; c, the extei'nal, and i, the internal 

 corpus-geniculatum ; h, the hypophysis 

 cerebri or pituitary body ; tc, tuber 

 cinereum with the infundibulum ; ,, 

 one of the corpora albicantia ; P, the 

 cerebral peduncle or crus ; III, close to 

 the left oculo-motor nerve ; x , the 

 posterior perforated space. 



The following letters and numbers refer 

 to parts in connection with the medulla 

 pblongata and pons. PV, pons Varolii ; 

 V, the greater root of the fifth nerve ; + , 

 the lesser or motor root ; VI. the sixth 

 nerve ; VII, the facialj VIII, the audi- 

 tory nerve ; IX., the 'glossopharyngeal ; 

 X, the pneumogastric nerve ; XI, the 

 spinal accessory nerve ; XII, the hypo- 

 glossal nerve ; C I, the suboccipital or 

 first cervical nerve ; p a, pyramid ; o, 

 olive ; d, anterior median fissure of the 

 spinal cord, above which the decussation 

 of the pyramids is represented ; c a, 

 anterior column of cord ; r, lateral tract 

 of bulb continuous with c I, the lateral 

 column of the spinal cord. 



oblongata (fig. 33) it is seen that the bundles of fibres of these nerve-roots traverse 

 the substance of the bulb to reach a group of nerve-cells in the grey matter near 

 the central canal and thus mark off a somewhat oval area on each side at the pos- 

 terior part of the section. This area is termed by Flechsig the posterior^ area of the 

 medulla oblongata, and the tracts of white fibres which can be traced, as will be 

 immediately noticed, upon the surface of this part, may therefore -be conveniently 

 termed its posterior columns. They correspond in position to the posterior columns 

 of the spinal cord. 



The line of origin of the anterior roots of the spinal nerves, although not marked 

 in the spinal cord by a distinct furrow like that whence the posterior roots issue, yet 

 when traced upwards into the bulb, deepens into a well-marked longitudinal groove 

 which is continued almost vertically as far as the lower border of the projecting 

 mass of the pons. In its upper part this groove separates the olivary pro- 

 minence from the prominence of the pyramid. Just below the olive it is often 

 obliterated for a certain part of its course by a band of transverse fibres. The root- 

 bundles of the hypoglossal nerve (figs. 32, 33, 34, XII) pass out from this furrow, 



