354 



PRACTICAL HISTOLOGY. 



[xxxi. 



centre at intervals into the grey matter, and run outwards as 

 medullary rays between the nerve-cells. By other methods it can 

 be shown that some of them become continuous with axis-cylinder 

 processes of the pyramidal and polymorphous cells, while, as shown 

 in fig. 331, others end in free arborisations. Tracing the fibres the 

 other way, i.e., as axial-cylinder processes of pyramidal cells, it has 

 been shown by other methods that some of them chiefly from the 

 large pyramids of the motor areas pass into the white matter, 

 enter the corona radiata, and pass through the inner and anterior 

 two-thirds of the posterior division of the internal capsule to enter 

 and form the pyramidal tracts. They constitute the projection 

 fibres, and end in free arborisations in relation with the multi- 

 polar nerve-cells of the anterior cornu of the grey matter of the 

 cord. 



The so-called commissural or callosal fibres, which join opposite 

 halves of the brain, pass into the corpus callosum either directly or 

 by collateral fibres (fig. 331) and pass to the opposite side to end as 



FIG. 329. Injected Cerebral Cortex of Dog. i. Layer with few vessels ; 2. Layer of large 

 pyramidal cells ; 3. Deepest layers of cortex ; 4. Medulla. 



free arborisations in the grey matter there (fig. 331, /). Others are 

 said to join the antero-posterior fibres (fig. 331, B) or association 

 fibres, which run between grey matter in different parts of the same 

 hemisphere. 



6. V.S. Middle Frontal Convolution (fig. 328). Compare this 

 with that from a motor area, and note the absence of the very large 

 pyramidal cells. In the gyms hippocampi or uncinate gyrus there 

 are other peculiarities, its grey matter consisting of numerous 

 conical cells with very long processes. It is hardened in the same 



