552 THE SPINAL CORD. 



The gray matter contains many other small nerve-cells, which we are not 

 able at present to name or arrange, but whose existence must always be 

 borne in mind. Confining ourselves now, however, to the groups of larger, 

 more conspicuous nerve-cells, we find that, broadly speaking, the chief dif- 

 ferences which can be observed in the cells of the anterior horn along the 

 length of the cord are that in the thoracic region the nerve-cells of the ante- 

 rior horn are few and relatively small, while in the cervical and lumbar 

 region, especially in the latter, they are numerous and large. It is not easy, 

 even if possible, to distinguish in the thoracic region the several groups of 

 cells marked in Figs. 12l"and 122 as 2 oc, [1, y the median group (Figs. 121, 

 122, 1), indeed, seems to be the only group present in the mid-thoracic 

 region (Fig. 119, 1). The group of the posterior horn (Figs. 119, 121, 122, 

 6) appears to be about the same in all regions. 



With two other groups of nerve-cells striking differences are seen in dif- 

 ferent regions. The vesicular cylinder, for instance (Fig. 119, 3), is most 

 conspicuous in the thoracic region. It may be said to reach from the 

 seventh or eighth cervical nerve to the third lumbar nerve, being perhaps 

 most developed in the lower thoracic and upper lumbar region. It is 

 absent in the cervical region above the seventh or eighth cervical nerve, and 

 in the lumbar region below the third lumbar nerve ; but a similar group of 

 cells is present opposite the second and third cervical nerves ; a group of 

 more doubtful likeness is seen in the sacral region below, and the column is 

 said to have a representative in the bulb above the spinal cord proper. It 

 seems natural to infer that the cells forming this vesicular cylinder are 

 connected neither with the ordinary somatic motor fibres governing the 

 skeletal muscles, nor with the ordinary afferent sensory somatic fibres 

 coming from the skin and elsewhere, but in some way with some special 

 sets of fibres ; on this point, however, no authoritative statement can as yet 

 be made. 



The lateral horn or intermedio-lateral tract (Fig. 119, 4) is also most con- 

 spicuous in the thoracic region. In the lumbar region it is lost or traced 

 with great difficulty, and in the cervical region seems to be merged into the 

 most dorsally placed division of the lateral group of cells of the anterior 

 horn. It is possible that this group represents in the limbless thoracic 

 region the cells which are developed into the great lateral group of the ante- 

 rior horn in the regions of the limbs. 



487. The white matter, as we have seen, increases in sectional area 

 with considerable regularity from below upward. If, instead of a diagram 

 of the increase of the whole white matter 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. 128) increases 

 with some considerable regularity from below upward, though not so regu- 

 larly as does the whole area of white, matter, both the anterior (Fig. 129) 

 and the posterior (Fig. 130) columns agree to a certain extent with the gray 

 matter in showing a decided increase in both the lumbar and the cervical 

 swellings. We may, provisionally at least, infer from this that, while con- 

 siderable portions of both the anterior and the posterior columns are, like 

 the adjoining gray matter, in some way or other concerned in the exit and 

 entrance of efferent and afferent fibres, the larger portion of the lateral 

 column is concerned in the transmission of impulses to and fro, between the 

 local mechanisms below, immediately connected with the several spinal 

 nerves, and the brain above. This conclusion seems incidentally confirmed 

 (though these diagrams must not be strained to carry detailed inferences) by 

 the sudden increase of the lateral column above the lumbar swelling, as if 

 the large mass of nervous mechanism for the lower limbs concentrated in 



