. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. NERVOUS CENTRES. (HUMAN ANATOMY. THE MENINCES.) 635 The surface of each choroid plexus presents many slight projections or folds resembling villi, in which are contained loops and plexi- form anastomoses of minute vessels, very si- milar to the arrangement of the vessels of the villous processes of the chorion of the ovum, or those of the tufts of the placenta. These vessels are surrounded by an epithelium which has much the appearance of that of serous membranes. From the great number of these vessels and from the delic
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. NERVOUS CENTRES. (HUMAN ANATOMY. THE MENINCES.) 635 The surface of each choroid plexus presents many slight projections or folds resembling villi, in which are contained loops and plexi- form anastomoses of minute vessels, very si- milar to the arrangement of the vessels of the villous processes of the chorion of the ovum, or those of the tufts of the placenta. These vessels are surrounded by an epithelium which has much the appearance of that of serous membranes. From the great number of these vessels and from the delicate nature of the epithelial covering which surrounds them, it is plain that the choroid plexuses are well suited either for the purpose of pouring out fluid or of absorbing it. Fig. Side view of villi of the choroid plexus of the lateral ventricle in the brain of a Goose, to show the disposition of the bloodvessels. Not to obscure the mew of t/te bloodvessels, the edge of the epithelium only has been shown. a, epithelium ; b, bloodvessels. (After Valentin.) The epithelium may be best seen by examin- ing the edge of a fold. It becomes very distinct when acted upon by acetic acid. As its particles are very delicate and consist only of a single layer, they are easily detached. The cells of epithelium are most of them six-sided, and contain a clear nucleus, or several minute gra- nules. Valentin states that cilia may be seen playing upon this surface, especially in the embryo. I have observed the peculiar punc- tiform or spiniform formations to which he alludes, which look like the remains of former vibratile cilia. Velum interposition. (Toile Choroidienne, Vicq d'Azyr.)—The choroid plexuses are con- nected to each other by the velum interpositum, which is a triangular fold of pia mater that passes in at the transverse fissure between the upper surface of the tubercula quadrigemina and the posterior reflected portion of the corpus callosum. This process is continuous with
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