THE VELUM IXTEKPOSITUM. 



763 



The VELUM IXTERPOSITUM (fig. 276, g) is the fold of pia mater Velum, or 

 entering the great transverse fissure. Triangular in shape, it has m ate r pl 

 tlu- same extent as the body of the fornix, and reaches in front to 

 the foramen of Monro. The upper surface is in contact with the 

 fornix, to which it supplies vessels. The lower surface, looking to is over third 

 the third ventricle, covers the pineal body and a part of each optic ve c e ' 

 thalainus : on it, close to the middle line, are the two choroid 



FIG. 276. SECOND VIEW OF THE DISSECTION OF THE BRAIN, THE FORNIX 



BEING CUT THROUGH IN FRONT AND RAISED BACKWARDS. 



a. Fornix. 



b. Hippocampus major. 



c. Tifiiia hippocampi. 



d. Caudate nucleus. 



c. Optic thalamus. 

 f. Choroid plexus. 

 y. Velum interpositum. 



plexuses of the third ventricle ; and along each side is the choroid and carries 

 plexus of the lateral ventricle. pSses. 



The CHOROID PLEXUS OF THE LATERAL VENTRICLE (fig. 276, /) Choroid 



is the red, somewhat rounded and fringed margin of the velum inter- p ^ ex j u ! of i 

 positum, which projects into the lateral ventricle, extending from ventricle, 

 the foramen of Monro to the extremity of the descending cornu. 

 Its lower part is larger than the upper. The epithelium lining the 

 ventricle is continued over the choroid plexus, but it loses its cilia 

 in this situation. The right and left choroid plexuses are continuous 



