الفهرس 
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Abstract
According to Sisson (1953), Millen and Woollam (1953) and Dohrmarn (1970a),jn domestic animals, important folds of the pia mater extend into two of the great fissures of the brain. One of these, passes in at the transverse fissure between the cerebellum and the cerebral hemisphere and is continued so as to overlie the 3rd ventricle forming the tela choroidea of that cavity. The second fold passes in at the transverse fissure between the cerebellum and the medulla oblongata forming the tela choroidea of the 4th ventricle. They constitute paths for the deeper vessels and their edges contain vascular convolutions which are known as the choroid plexuses,
The recess between the lateral aspect of the medulla and the cerebellum is occupied by an irregular mass of v-illous projections of the pia mater containing tufts of blood vessels, this is the choroid plexus of the 4th ventricle. The pie mater forms three fringed masses which contain vascular convolutions and are designated as the median and lateral choroid plexuses of the 4th ventricle, They appear to lie within the ventricle but are realy excluded from the cavity by the epithelial lining which they invaginate. The choroid plexus of the 4th ventricle is relatively larger and e%tend caudally through the lateral apertures (forarnena of Luschka) of the 4th ventricle.
The 3rd ventricle is a narrow annular space between the thalami. It corirnunicates, by means of the cerebral aqueduct, with tha 4th ventricle behind0 In front, it is continuous with the lateral ventricle on each side through the interyentrjcular foranien (foramen of Monro). The roof of the 3rd ventricle is invaginated by 2 delicate choroid plaxuses which appear to lie within the ventricle although they are separated fron the cavity by epitheliuzn,
The lateral ventricle is an irregular cavity in the interior of each cerebral hemisphere. Each communicates with the 3rd ventricle through the interventricular foramen. It consists of a central part or body, and anterior and ventral horns. The roof of the ventricle is formed by the corpus callosum and the medial wall by the septum pellu— cidum. The floor is formed by two bodies; the anterior body is the caudate nucleus and the posterior body is the hippo— campus. The 2 bodies are separated by an oblique groove which is occupied by the choroid plexus of the lateral ventricle.