SPINAL CORD AND COMMENCEMENT OF MEDULLA OBLONGATA. 185 



assigned to each. Please notice in this, as in the last figure, how 

 the tracts which decussated in the spinal cord and those which 

 ascended directly are united to form a single body. We have 

 now met with two important 

 decussations, that of the pyra- 

 mids and that of the lemniscus. 

 The former is composed of motor 

 fibres, while the latter contains 

 the sensory tracts. 







There are formed, therefore, 



two new large tracts of fibres, 

 which lie in the ventral portion 

 of the oblongata, viz., the pyra- 

 midal columns, and, dorsad of 

 these, the layer of the fillet, or 

 inter-olivary layer. We shall 

 find them both occupying the 

 same relative position as far up 

 as the corpora quadrigemina. 



The transverse area of the 

 layer of the fillet is, in adults, 

 much richer in fibres than is 

 shown in the illustrations, which 

 have been prepared from sec- 

 tions taken from the foetus. In 

 the latter none of the sensory 

 fibres from the antero-lateral 

 columns are medullary, and only 

 those bundles which come from 

 the nuclei of the posterior 

 columns can be seen. 



The whole configuration of the section is changed by these 

 two decussations. In addition to this the gray matter, as I will 

 presently show you, varies its outline. New masses of gray 

 matter appear in the oblongata. We have already met three 



FIG. 111. 



Diagram of the course of the sensory 

 tract from the posterior roots to the medulla 

 oblongata. 



Kleinhirn-S6iten J3., Lateral oerel>ellnr tract. 

 V'urtler-Seitenstr., Antero-lateral column. 



