CHAP, i.] THE SPINAL CORD. 693 



ner. This is strikingly shewn by comparing Figs. 110, 111 and 

 112. At the level of the third lumbar nerve (Fig. 112) the grey 

 matter is very large, reaching, as we have seen, its maximal 

 sectional area at about this point, so that although the area of 

 white matter is not very great the whole area of the cord is 

 considerable. 



At the level of the sixth thoracic nerve (Fig. 110), in spite 

 of the white matter having very decidedly increased, the grey 

 matter has shrunk to such very small dimensions, that the 

 total sectional area of the cord has markedly diminished. 



At the level of the sixth cervical (Fig. Ill) the grey matter 

 has again increased, reaching here as we have seen its second 

 maximum ? the white matter has also further increased, and 

 that indeed very considerably, so that the total area of the 

 cord is much greater than in any of the lower regions. 



Further details of the varying size of the white matter and 

 of the grey matter at different levels are also shewn in the 

 series given in Fig. 114. In these, combined with the three 

 figures just referred to, it will be observed that the serial in- 

 crease and decrease of the grey matter does not affect all parts 

 of the grey matter alike, so that the outline of the grey mat- 

 ter changes very markedly in passing from below upwards. 

 In the coccygeal region each lateral half is a somewhat 

 irregular oval, and in the sacral region, Fig. 114, Sac, 

 the differentiation into anterior and posterior horns is still 

 very indistinct. In the lumbar region the two horns are 

 sharply marked out, though both the posterior and anterior 

 horns are broad and more or less quadrate. In the thoracic 

 region the decrease of grey matter has affected both horns, so 

 that both are pointed and slender, while the junction between 

 them has not undergone so much diminution, so that what has 

 been called the lateral horn is relatively conspicuous. In the 

 cervical region the returning increase bears much more on the 

 anterior horn which again becomes large and broad, than on 

 the posterior horn which still remains slender and pointed. 

 Taking the form of the grey matter in the thoracic region as 

 the more typical form of the grey matter we may say that 

 while the increase on the lumbar swelling bears equally on 

 the anterior and posterior horns, that in the cervical region 

 bears chiefly on the anterior horns. 



456. The white matter as we have seen increases in sec- 

 tional area with considerable regularity from below upwards. 

 If instead of a diagram of the increase of the whole white mat- 

 ter, we construct in a similar way diagrams of the anterior, 

 posterior and lateral columns respectively we find that while 

 the sectional area of the lateral column (Fig. 118) increases 

 with some considerable regularity from below upwards, though 

 not so regularly as does the whole area of white matter, both 



