674 A MANUAL OF PHYSIOLOGY 



Arrangement of the Grey and White Matter in the Spinal 

 Cord. The grey matter of the spinal cord is arranged on 

 each side in a great unbroken column of roughly crescentic 

 section (Plate V., 3), joined with its fellow across the middle 

 line by a grey bar or bridge, which springs from the con- 

 vexity of the crescent, and is pierced from end to end by 

 the central canal. The anterior horn of the crescent, 

 although it varies in shape at different levels of the cord, is, 

 in general, broad and massive in comparison with the 

 slender and tapering posterior horn. In the lower cervical 

 and upper dorsal region a moulding or projection, forming 

 a lateral horn, springs from the fluted outer side of the grey 

 substance. Within the grey matter nerve-cells are found, 

 sometimes so regularly arranged that they form veritable 

 cellular or vesicular strands. Of these the best marked are : 

 (i) The tract or tracts made up by the cells of the anterior 

 horn (Fig. 238), which practically run from end to end of the 

 cord, swell out in the cervical and lumbar enlargements, 

 where the cells are very numerous and of great size (70 //, to 

 140 IJL in diameter), and contract to a thin thread in the 

 thoracic region, where they are relatively few, scattered, and 

 small. (2) Clarke's column, whose cells are situated at the 

 inner side of the root of the posterior horn just where it 

 joins on to the grey cross-bar. It gradually increases in size 

 from above downwards, usually appearing first at the level of 

 the seventh or eighth cervical nerve, attaining its maximum 

 development at the eleventh or twelfth dorsal and dis- 

 appearing altogether, as a continuous strand, at the level of 

 the second or third lumbar nerves. Scattered nerve-cells, 

 however, constituting the so-called cervical and sacral nuclei 

 of Stilling, are frequently found occupying the same position 

 towards the upper and lower ends of the cord, and may be 

 looked upon as isolated portions of Clarke's column. (3) A 

 tract called the intermedia-lateral tract, situated at the outer 

 edge of the grey matter, about midway between the anterior 

 and posterior horns. It is best marked in the thoracic region, 

 but extends also down into the lumbar swelling and up until 

 it blends with certain cells of the anterior horn of the cervical 

 cord. (4) The cells of the posterior horn are less numerous 



