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386 Veterinary Histology of Domestic Mammals and Birds

spinal cord and brain stem, where the nerve fibre-rich
VetBooks.ir white matter is located superficially while the grey matter
lies internally, adjacent to the central canal and ventricles).
The basal nuclei of the cerebrum are also composed of
grey matter. White matter makes up the interior of the
cerebrum. The fibres of the white matter establish connec-
tions within the main bulk of the brain. Tracts formed by
processes extending from efferent cells and interneurons
of cranial nerves, and from projection neurons from the
spinal cord, connect the components of the brain to form
an integrated functional system.

Cerebral cortex (cortex cerebri)
The structure of the cerebral cortex (neocortex, isocor-
tex) (Figures 17.9 to 17.11) exhibits regional variation in
nerve cell, fibre bundle and glial cell architecture, and in
the organisation of blood vessels. Nevertheless, all regions
conform to a basic structural plan. In mammals, the cere-
17.7 Grey matter of the cerebellum (cat). Bodian stain bral cortex is composed of six layers. From superficial to
(x300). deep, these are the:

Golgi cell dendrites extend into the molecular layer where · molecular layer (stratum moleculare),
they divide into branches. · external granular layer (stratum granulare
externum),
Cerebrum · external pyramidal layer (stratum neuronorum
The neural components of the cerebrum vary in size, den- pyramidalium externum),
sity, morphology and structure, reflecting the number and · internal granular layer (stratum granulare internum),
complexity of the functions performed by this part of the · internal pyramidal layer (stratum neuronorum
central nervous system. This accounts for the considerable pyramidalium internum) and
differences in cyto-architecture observed within individual · multiform layer (stratum neuronorum multifor-
layers in some parts of the brain. Marked variation also mium) (Figure 17.9).
occurs in the organisation of glial tissue, vessels and nerve
fibres. The outermost molecular layer is covered by the pia
Like the cerebellum, the cerebrum has an external mater. Scattered small neurons (neurona horizonta-
cortex composed of grey matter (this contrasts with the lia) give off myelinated axons that course parallel to the

17.8 Layers of the cerebellum (schematic).

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