304 LECTURE XIII. 



alone that we can detect in this spot the transverse section 

 of the canal in the shape of a minute hole (Fig. 90, c, c), 

 which, like nearly all the free surfaces of the body, is in- 

 vested with a layer of epithelium. It has now taken up 

 its stand as a really regular, constant and persistent ca- 

 nal. It is continued throughout the whole extent of the 

 spinal marrow from the filum terminale, where it cannot 

 at all times be very distinctly demonstrated, up to the 

 fourth ventricle, where the orifice by which it opens into 

 the so-called sinus rhomboidalis* is situated in the gela- 

 tinous substance of the calamus scrip torius. Here it may 



FIG. 90. 



Fig. 90. The half of a transverse section from the cervical part of the spinal mar- 

 row, fa. Anterior fissure ; fp, posterior fissure, cc. Central canal with the 

 central thread of ependyma. ca. Anterior commissure with nerve-fibres crossing 

 one another ; cp, posterior commissure, ra. Anterior roots ; rp, posterior ones. 

 gm. Accumulation of motor cells in the anterior horns ; gs, sensitive cells of the 

 posterior horns ; gs', sympathetic cells. The black, dotted mass represents a trans- 

 verse section of the white substance of the cord (the nerve-fibres belonging to the 

 anterior, lateral and posterior columns) and its lobular divisions. 12 diameters. 



* A name given to the floor of the fourth ventricle. 



