Human anatomy, including structure and development and practical considerations . page 1044), arises as the axonesof these neurones. The anterior reflex fibres to the ventral horn are all collaterals, not continu-ations of the stem-fibres, far the greater part of which come from the fibres of thelong ascending posterior tract. These collaterals penetrate the gray matter princi-pally at the median border of the head of the posterior horn, behind Clarkescolumn, but partly also through the substantia Rolandi, and thence pass ventrally orventro-laterally, with a slightly curved or sigmoid course,
Human anatomy, including structure and development and practical considerations . page 1044), arises as the axonesof these neurones. The anterior reflex fibres to the ventral horn are all collaterals, not continu-ations of the stem-fibres, far the greater part of which come from the fibres of thelong ascending posterior tract. These collaterals penetrate the gray matter princi-pally at the median border of the head of the posterior horn, behind Clarkescolumn, but partly also through the substantia Rolandi, and thence pass ventrally orventro-laterally, with a slightly curved or sigmoid course, towards the anterior they enter the latter, the collaterals diverge more and more and are distributedto the various groups of the anterior horn cells, chiefly in relation with the lateralgroups of radicular cells from which the ventral root-fibres arise ; they thus establishdirect reflex paths by which sensory impulses conveyed by the posterior root-fibresimpress the motor neurones, while, at the same time, these impulses are transmitted 66 1042 HUMAN ANATOMY FiG. Section of spinal cord at level of sixth cervical segment; anteriorcomua are very broad ; obliquely cut bundles of posterior root-fibres lie inposlero-lateral sulcus. Preparation by Professor Spiller. X 6. to lii^hcr levels by the ascendintj steiii-fihres. Althcjiigh the anterior reflex collat-erals are, for the most part, in relation with the cells of the same side, it is probablethat some cross by way of the posterior commissure, and possibly also by the anteriorbridjjc, to the opposite ventral horn cells. It is doubtful, on the other hand,whether either stem-fibres or collaterals of the j)osterior roots pass directly to theanterior column either of the same or opposite sides ( Ziehen). The root-fibres passing to the posterior horn include those which pene-trate the substantia Rolaiuli, either as collaterals or stein-tihres of Hurdachs or of Lissauers tracts, to endabout the neurones withinthe Rolandic
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