206 



THE ESSENTIALS OF HISTOLOGY 



large number of small nerve-cells with reticulating bundles of medul- 

 lated nerve fibres running between them. 



2. An intermediate nerve-cell layer (6) consisting of neuroglia, in 

 which small pyramidal nerve -cells are embedded. This layer is also 

 traversed by medullated nerve-fibres, and is partly separated from the 

 granule layer by irregular clefts (5). 



3. The layer of olfactory glomeruli (7) consists of rounded nests of 

 small ganglion-cells, which appear to give origin to the olfactory nerve- 

 fibres. These pass between the glomeruli to enter the close plexus of 

 non-medullated nerve-fibres which lies directly over the cribriform plate. 



4. This is the layer of olfactory nerve-fibres (s), and from it 

 branches (*) pass directly downwards to the nasal fossas. 



Utt 



FIG. 242. SECTION ACROSS A PART OF THE OLFACTORY BULB. 



1, 3, bundles of very fine transversely cut nerve-fibres, forming the flattened medullary ring, 

 enclosing the central nouroglia, 2 ; 4, granule-layer; 5, loose tissue with irregular spaces 

 (? lymphatic) ; 6, intermediate layer; 7, layer of olfactory glomeruli, t, tt ; 8, layer of 

 olfactory nerve-fibres. 



Basal ganglia. Besides the grey matter of the cerebral cortex the 

 cerebral hemispheres conceal in their deeper parts certain other masses 

 of grey substance (fig. 243). The principal of these are the corpus 

 striatum (nucleus caudatus, c, and nucleus lenticularis , sir) and optic 

 thalamus (th). Between them run the bundles of white fibres which are 



