468 THE ORGAXS 



only in the cervical cord (Fig. 319 and 323). Here the most median 

 fibres, i.e., those lying in the column of Goll, are the longest fibres of 

 the posterior columns, having come from the lower spinal ganglia 

 (lower thoracic, lumbar and sacral), while the column of Burdach 

 (Fig. 319) consists of short and medium length fibres (upper thoracic 

 and cervical dorsal root fibres). The fibres of Goll's column end 

 in the nucleus Juniculi gracilis or nucleus of the column of Goll in 

 the medulla (see p. 491 and Fig. 334). Those fibres of Burdach's 

 which do not terminate in the spinal cord terminate in the medulla 

 in the nucleus funiculi cuneati or nucleus of the column of Burdach 

 (p. 491 and Fig. 334). The nucleus gracilis and nucleus cuneatus — 

 which will be seen in sections of the medulla (Fig. 334) — thus serve 

 as terminal nuclei for the afferent root fibres in the columns of Goll 

 and those of the columns of Burdach which do not terminate within 

 the cord. Inasmuch as many of the ascending arms are short, it is 

 evident that only a fraction of the dorsal root fibres are represented 

 at the higher levels. Those long arms which reach the medulla con- 

 stitute the beginning of one of the principal afferent cerebral or pallial 

 pathways. The axones of the neurones, whose bodies are the nuclei 

 of Goll and Burdach, cross and form the tract known as the medial 

 fillet (or lemniscus), composing the second system of this path. The 

 fillet terminates in the thalamus and the path is completed by a third 

 system of thalamo-cortical neurones to the cortex pallii, (probably 

 principally to the post-central area). This path is, in brief, as fol- 

 lows: spinal ganglionic (long ascending arms of dorsal roots) + 

 fillet + thalamo-cortical path, decussating in the medulla (Fig. 330). 



II. The Spine -thalamic Tract.- — This arises from heteromeric cells 

 lying probably principally in the dorsal horn (groups c and d, p. 456). 

 Their axones cross in the ventral commissure and reach the opposite 

 lateral funiculus where they ascend in a position mesial to the ventral 

 spino-cerebellar tract (see below). This tract terminates in the 

 thalamus whence the path is completed by thalamo-cortical neurones. 

 The path is thus: spinal ganglion (short arms and collaterals of dorsal 

 roots) + spinothalamic -j- thalamo-cortical neurones, three systems of 

 neurones. Its decussation takes place in the cord at about the level 

 of entry of the dorsal roots involved. Associated with this system 

 may be some fibres to the superior colliculus (spino-collicular tract). 

 (Figs. 326, 327 and 331). 



B. Tracts forming part of paths to the cerebellum. 



