CHAP, i.] THE SPINAL CORD. 885 



573. The changes in the area of grey matter illustrated by 

 the statements and diagrams given above refer to the grey matter 

 as a whole, that is, not only to nerve cells, but also to strands 

 and networks of nerve fibres and nerve fibrils, and indeed include 

 to a certain extent neuroglia. We have seen 566 that we are 

 able to distinguish certain large and conspicuous nerve cells in 

 the grey matter and to arrange these into groups. The grey 

 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 differences 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 anterior 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 negion 

 the several groups of cells marked in Figs. 98, 99 as 2a, yS, 7 ; the 

 median group (Figs. 98, 99, 1), indeed seems to be the only group 

 present in the mid thoracic region (Fig. 96, 1). The group of the 

 posterior horn (Figs. 96, 98, 99, 6) appears to be about the same 

 in all regions. 



With two other groups of nerve cells striking differences are 

 seen in different regions. The vesicular cylinder, for instance 

 (Fig. 96, 3), is most conspicuous in the thoracic region. It may 

 be said to reach from the 7th or 8th cervical nerve to the 3rd 

 lumbar nerve, being perhaps most developed in the lower thoracic 

 and upper lumbar region. It is absent in the cervical region 

 above the 7th or 8th cervical nerve, and in the lumbar region 

 below the 3rd lumbar nerve ; but a similar group of cells is 

 present opposite the 2nd and 3rd 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. 96, 4 is 

 also most conspicuous 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 the 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 anterior 

 horn in the regions of the limbs. 



