OTTO u 



MEDULLA OBLONG ATA 167 



degenerate in the cord and seem to be comraissural between 

 different levels of the grey matter (see p. 167). 



Other tracts of fibres have been described, such as Lis- 

 sauer's tract and the septa-marginal tract, but their relations 

 have not been satisfactorily investigated. 



B. THE MEDULLA OBLONGATA 

 1. Structure 



The medulla oblongata may be regarded as the upper end 

 of the spinal cord, which it connects with the brain (fig. 83). 

 The cord expands and the dorsal median fissure is opened 

 out, so that the central canal comes to the surface, and 

 expands into a lozenge-shaped area the floor of the fourth 

 ventricle. The lateral columns of the cord pass outwards 

 tc the cerebellum to form part of its inferior peduncles 

 the restiform bodies. Between the lateral and the ventral 

 columns an almond-shaped swelling, the olive, appears (fig. 

 85, 0.). In front of this the medulla is encircled by a mass 

 of transverse fibres the middle peduncles of the cerebellum, 

 or the pons Varolii (fig. 87, P.}- The floor of the fourth 

 ventricle is constricted above by the approximation of the 

 superior peduncles of the cerebellum (fig. 83, p.c.s.) to again 

 become a canal. The grey matter of the cord gets broken up 

 into separate masses, of which the most important are 



1. The nuclei of the dorsal columns the nucleus gracilis 

 and nucleus cuneatus (fig. 84, N.C. and N.Gr.} masses of cells 

 and synapses in which the fibres of the dorsal columns end, 

 and from which the upgoing fibres of the fillet start. 



2. The inferior olivary nucleus (fig. 85, 0.), which lies in 

 the olive, and which is connected by bands of fibres with the 

 dentate nucleus of the cerebellum (fig. 87, Dent.). 



3. The nucleus of Deiters (fig. 87, Deit.), lying higher up in 

 the pons Varolii, and connected with fibres from the cerebellum 

 and from the semicircular canals (see fig. 81). 



4. The nuclei of the cranial nerves, masses of cells from 

 which the nerves take origin (fig. 86). 



