464 THE PINEAL ORGAN 



obstructed, and there was no marked distension of the third or lateral ventricles 

 (Fig. 316). The pia mater around the pineal body and neighbouring parts was 

 considerably thickened. 



The pineal cyst was removed for microscopical examination and serial 

 longitudinal sagittal sections were cut and stained with hematoxylin and eosin 

 and with picro-indigo-carmine. 



These showed that the cavity of the cyst was formed by the breaking down 

 of the central part of the pineal body. Its wall showed, in a modified form, 

 the structure of the pineal gland (Fig. 317, A). There was a pseudo-epithelial 

 stratum lining the cavity, the tissue immediately bounding the lumen being 

 fibrillar and glial in nature. A middle zone, which formed the major part of 



Fig. 314. — Case 8. Radiograph 

 demonstrating hammer mark- 

 ing owing to the increased 

 Intracranial Pressure due to 

 a Pineal Tumour. 



Fig. 315. — Case 8. Histological 

 Picture showing Appearance of 

 a Pineal Tumour ( 320). 



the thickness of the cyst wall, showed typical parenchymatous pineal cells. 

 These were of small size, but had relatively large nuclei ; they were imbedded 

 in a loose glial network, which forms the supporting tissue throughout the whole 

 thickness of the cyst wall. 



There were some irregular plaques of calcareous deposit in the wall of the 

 cyst, and corpora arenacea were abundant in the surrounding membranes, 

 but were not present in the actual wall of the cyst. 



Lying dorsal to the pineal body was a tubular diverticulum of the ependyma, 

 which extended the whole length of the pineal body (Fig. 318). It opened 

 into the third ventricle at the suprapineal recess, and contained groups of 

 choroidal villi, which projected into its lumen (Fig. 317, B). This represents 

 the persistent dorsal sac which is present in foetal life, and is formed as a tubular 

 outgrowth from the roof of the posterior part of the third ventricle. It would 

 probably have contributed to the secretion of the cerebrospinal fluid. Should 

 its opening have become blocked, it might have given rise to a thin-walled 

 cyst, which would have differed from the pineal cyst described above in having 



