302 MANUAL OF HISTOLOGY. 



to the undivided dura mater. Thus prepared it is suspended 

 in Miiller's fluid (see p. 15), or dilute chromic acid (see p. 

 14), until hardened. The segments are then embedded in 

 a microtome (see p. 16), and horizontal, transverse sections 

 made. These are washed in distilled water and stained with 

 carmine or hsematoxylon (see p. 23). A few minutes' immer- 

 sion in alcohol previous to this manipulation makes the tissues 

 take the coloring more quickly. After staining and washing, 

 dehydrate the sections with alcohol and absolute alcohol, make 

 transparent with oil of cloves, and mount in Canada balsam or 

 dammar varnish (see p. 23). 



Hidden in the cauda equina is found the filum terminale, 

 which is the end of the cord. Sections near its end exhibit lit- 

 tle of the structure of the cord. At a point where it is 1.5 mm. 

 in diameter it presents the appearance of a peripheral nerve, 

 except that it has an opening the central canal in its centre. 

 Its transverse section shows a collection of large and small 

 myelinic nerve-fibres pursuing a vertical direction. 



A little higher up, where the filum measures 2 mm. in diam- 

 eter, there is little difference, except that the central canal is 

 nearer the surface (anterior) and surrounded by a small amount 

 of gray matter. Now and then there are seen small, oval nerve- 

 cells in the region posterior and external to the central canal. 

 A little higher still, where the filum is 3 mm. in transverse 

 and 2 mm. in antero-posterior diameter, back ' of the central 

 canal on each side, where the future posterior horn is to be, 

 there is a small collection of spindle-shaped cells. 



Sections from a region a little above this present an entirely 

 different picture. The gray substance is here much more devel- 

 oped and occupies the larger part of the section. It is divided 

 into a club-shaped anterior horn, containing a few large poly- 

 hedral cells, and a posterior horn which is rounded and formed 

 of peripherally directed nerve-fibres and oblong nerve-cells. 

 From this point up sections gradually become more circular 

 and develop more and more a resemblance to the structure of 

 the cord, until, at a point where the sections are about 3.5 mm. 

 in diameter, the anterior fissure and posterior septum become 

 well marked. The anterior horns contain few cells, and the 

 fibres emanating from them pursue a very oblique course down- 

 ward through the anterior columns. 



From the lateral gray matter arise bundles of nerve-fibres 



