286 MICROSCOPIC ANATOMY OF THE ORGANS. 



of the processes, we speak of astrocytes with long rays or short 

 rays. 



The glia fibres, which formerly were believed to be cell 

 processes, are to be considered as entirely independent ele- 

 ments. They react to certain coloring reagents quite differ- 

 ently from the cell protoplasm or its processes, and pass through 

 the cell body, so that their course can be followed uninter- 

 ruptedly. They usually run through the outer layers of the 

 cell body or lie on the cells. They are probably products 

 of the cells which have become so much emancipated from the 

 cell body that some of them seem to have no definite con- 

 nection with the cell. These fibres are of different thicknesses 

 and form a dense network. A considerable aggregation of 

 neuroglia is found around the larger nerve cells, in the region 

 of larger vessels, and especially around the central canal (cen- 

 tral glia-mass, substantia grisea centralis). It also occurs on 

 the periphery of the cord (superficial glia capsule). 



Concerning the significance and function of the neuroglia, 

 many theories have been advanced. According to Golgi, the 

 neuroglia serves as a source of nourishment for the nerve cells. 

 Ramon y Cajal claims that it has an insulating function in 

 connection with the neurones. Weigert considers that it serves 

 only as a supporting tissue to fill up the spaces between the 

 neurones. According to K. Krause, the cells and fibres form 

 paths for the circulation of lymph. 



For a detailed description of the medulla, pons, midbrain, 

 and the higher centres, the reader must be referred to special 

 text-books on the subject. 1 In the space at our disposal only 

 a brief account can be given. 



1 Barker, L. F.: Nervous System, Appleton, New York, 1899. 

 Kdini^cr: I5:iu dcr ncrvnsoi) ( 'entralorgane, Leipsic, 1893. 

 v. Kolliker: Handbuch d. Gewebelehre, Bd. II., Leipsic, 1896. 

 van Gehuchten : Anatomie du systeme nerveux de 1'homme, Louvain, 1897. 

 fcabin, F. K. : Atlas of Medulla and Midbrain, Baltimore, 1901. 



