APPENDIX. 537 



itself, I am unable to say, not having myself detected them 

 in either of the above situations. 



These bodies, which are almost peculiar to the human 

 subject, are stated not to occur in the pineal gland, until 

 after the age of seven years. 



In addition to the above described essential elements of 

 every fully formed human pineal gland, I encountered on one 

 occasion two large round cells or bodies containing dark 

 nuclei of a compound character ; these appeared to be some 

 modification of the sabulous bodies already described. 



The pineal gland is copiously supplied with blood vessels, 

 is traversed sparingly with delicate nerve tubules, and con- 

 tains a small quantity of an exceedingly slender form of 

 fibrous tissue, which possibly proceeds from the caudate cells 

 already noticed. 



The Pia Mater. 



The pia mater, the vascular membrane of the brain, is 

 composed of fibrous tissue and blood-vessels ; over the surface 

 of the brain and its convolutions, this membrane is delicate 

 and highly vascular, while over the spinal marrow, it is thicker 

 and less freely supplied with vessels. 



In the ventricles, this membrane forms the choroid plexuses 

 and velum interpositum ; in the former, it is thrown up into 

 numerous processes or villi, each of which is furnished with a 

 large looped blood-vessel, and its outer surface, like the villi 

 of the intestines, is clad with a very evident epithelium. 

 (Plate LXIX. fig. 9.) 



This epithelium, according to many observers, is of the 

 ciliated kind; the cells composing it, are polygonal, some- 

 what flattened, and as Henle* long since noticed, furnished 

 at their angles with spinous processes ; these are only to be 

 seen in perfectly fresh subjects, and it is probable that in 

 some cases, they have been mistaken for cilia ; not, however, 

 since the fact has been attested by several witnesses, that I 



* Anat. Gen. t. i. p. 233. 



