432 THE PINEAL ORGAN 



infiltrate into the surrounding tissue — the hemispheres, the cerebellum, 

 and the third ventricle — and tend to obliterate the aqueduct. Cysts are 

 often present and areas of haemorrhage occur. The surface is irregular 

 and lobulated ; cysts may be seen on the cut surface. 



Microscopically there is a marked variation in the type and arrange- 



Fig. 284. — A Transversely Striated Muscle-Fibre from the Epiphysis of 

 Bos taurus. (After Dimitrowa.) 



ment of cell found. The cells are arranged in a mosaic with streams of 

 small cells deeply staining in character and enclosing nests of larger cells 

 with vesicular nuclei and larger masses of clear cytoplasm, bearing a 

 strong resemblance to the parenchyma cells of the mature pineal body. 

 Giant cells are not an uncommon feature in various areas of these tumours ; 

 they are more common in the vicinity of the calcified plaques, which are a 

 frequent feature of such growths. 



