836 THE NERVOUS SYSTEM. 



through which they pass, though not infrequently nerves pass through 

 these tumors without being in the least involved in their peculiar struc- 

 ture. Paltauf has described as endotheliomata rare tumors of the glan- 

 dula carotica. 



PARASITES. 

 Cysticercus and more rarely echinococcus occur in the brain. 



HOLES AND CYSTS IN THE BRAIN. 



Larger or smaller holes may be found in the brain tissue from dilata- 

 tion of the perivascular lymph-spaces, or well-formed cysts may exist 

 as a result of haemorrhage, inflammatory softening, hydatids, etc. 



PORENCEPHALUS 



is a term which has had a wide range of application to various defects of 

 the brain substance. By some writers the term has been used to cover 

 almost any congenital absence of brain tissue. By others brain defects not 

 congenital are included. Its most common application is to certain quite 

 well-defined congenital conditions in which there is an absence of a con- 

 siderable portion of one or both hemispheres. These holes may lie deep 

 in the substance of the brain. More commonly they come to the surface 

 making conical depressions in the cortex, which the dura mater bridges 

 over, but into which the pia extends. There may or may not be commu- 

 nication with the ventricles. This condition may coexist with various 

 mental aberrations, hydrocephalus, etc. Similar defects may occur in 

 the cerebellum. 



Pineal Gland. 



This little body, about the size of a cherry stone, is composed of con- 

 nective tissue enclosing cavities, which are filled with reticulated tissue 

 and round cells. The cavities often contain brain sand. 



A small number of tumors belonging to the class of teratoma have 

 been described as originating in the pineal gland. 



Weigert 1 describes a tumor, about 3.5 cm. in diameter, composed of 

 epidermis, hair follicles, hair, sebaceous glands, cartilage, fat, sniot>th 

 muscle, and cylindrical epithelium. 



Falksou 2 describes a chondro-cysto-sarcoma, 5.8 cm. in diameter, 

 which apparently originated in the pineal gland. 



Turner 3 describes a tumor of the pineal gland, projecting into the 

 third ventricle and the left lateral ventricle, of the size of a kidney. The 



1 Virch. Arch., Ixv., p. 212. Ibid., Ixxv., p. 550. 



3 Trans. London Path. Soc., xxxvi. 



