16 THE SPINAL CORD. 



mesial group : on this account it is thought to give origin to the nerves which 

 supply the dorsal muscles of the spinal column. It is sometimes described as 

 forming two sub-groups, viz. : a dorso-mesial and a ventro-mesial. 



The ventro-lateral group probably gives origin to the nerves which supply the 

 lateral and ventral muscles of the trunk, including the muscles of respiration. In 

 the cervical region it is described as consisting of two parts, one more laterally 

 situated, which gives origin to fibres of the spinal accessory, and another, more 

 mesially placed, which is believed to give off the fibres of the phrenic nerve. In 

 the lumbar enlargement it also tends to be sub-divided. 



The dorso-lateral group is mainly developed in the cervical enlargement and 

 lumbar enlargement, and has an evident relationship to the nerve-roots of the 

 brachial and sacral plexuses. It also shows subordinate groupings, which probably 

 have special connections with particular groups of the limb-muscles. For various 

 conjectures regarding both these and other cell-groupings in the grey matter, the 

 reader may consult the paper by Kaiser, which is given in the Bibliography. 



Some of the cells which are nearer the anterior commissure send their axis- 

 cylinder processes through this commissure to the anterior white column of the 

 other half of the cord : it is believed that these processes may be connected with 

 nerve-fibres of the corresponding anterior root of the other side. 



In some of the lower vertebrates it may be made out that there are ^variations in the size 

 of the column of cells of the anterior horn in successive portions of the cord, the cells being- 

 more numerous opposite the points of entrance of the nerve-roots, the attachment of which 

 to the cord is in them more localized than in man and higher vertebrates. In this way some- 

 what of a segmental formation of the column is indicated, and in some fishes and reptiles 

 the enlargement of the group of cells and its enclosing grey matter is sufficiently marked to 

 produce an external swelling opposite each nerve-pair. A similar segmentation is indicated in 

 an early stage of development in all vertebrates, including man, by the fact that the cord is 

 somewhat enlarged opposite each pair of nerve-roots. 



Clarke's column. A second very well marked group or column of large cells, 

 which occupies in transverse section an area at the inner or mesial angle of the base 

 of the posterior horn (fig. 14,/), and appears cut off from the rest of the grey matter 

 by a curved bundle of fibres derived from the posterior root, extends along the 

 middle region of the cord from about the third lumbar to the seventh cervical 

 nerve. This was termed by Lockhart Clarke the posterior vesicular column; 

 it is usually known as Clarke's column, although the cells were first noticed by 

 Stilling. It is best developed in the lower part of the dorsal (thoracic) region. 

 Prom the fact that it is almost entirely confined to the thoracic region of the cord 

 it was termed by Stilling the " dorsal nucleus." But although ceasing above and 

 below the points mentioned, it is not altogether unrepresented in other parts, for 

 groups of cells are found in a similar situation opposite the origin of the second and 

 third sacral nerves (" sacral nucleus " of Stilling) and opposite the origin of the third 

 and fourth cervical nerves (" cervical nucleus ") ; and elsewhere there are scattered 

 cells of the same character in the same part of the section of the cord. The cells of 

 this column, like most, if not all, the cells of the spinal cord, are multipolar, and 

 their axis-cylinder processes tend towards the lateral column, where they are believed 

 to form the direct cerebellar tract (Flechsig). The cells themselves are surrounded 

 by a fine plexus of nerve-fibrils, probably derived from collaterals of the posterior 

 root-fibres. They are of large size, measuring, according to Mott, in their longest 

 diameter, which is directed longitudinally, from 40yu to 90/i, the largest being found 

 in the lowermost part of the column. In the foetus and even in the new-born child 

 they are much smaller (25/x to 30/j), but by the second or third year after birth 

 they have nearly attained the same size as in the adult. 



Lateral cell-column. A third column of cells lies in the intermedio-lateral 



