FIBRES OF THE MEDULLA OBLONGATA. 



735 



leclian fissure. The decussating fibres are the more numerous, and 



as* obliquely backwards, across the median fissure and behind the and crossed. 



sposite anterior column, to enter the lateral column of the cord, where 



ley constitute the crossed pyramidal tract. Upwards, the fibres of the 



yramid are prolonged through the pons to the crusta of the cerebral 



eduncle (fig. 263, c, d}. The fibres of the anterior column of the Rest of 



ml which are not continued into the pyramid incline backwards, 



FIG. 264. DEEP DISSECTION OF THE MEHU 

 CRUS CEREBRI. 



JLONGATA, PONS, AND 



a. Pyramidal fibres, cut through, 

 id raised as far as the optic 

 alamos. 



b. Lateral tract. 

 t 1 . Olivary body. 



d. Deep longitudinal fibres in the 

 .s. derived from the anterior and 



lateral columns of the cord. 



e. Superficial, and /, deep trans- 

 verse fibres of the pons, cut through, 

 and partly removed. 



g. Substautia nigra in the crus 

 cerebri, between the crusta and 

 tegmeutum. 



id enter the reticular formation (fig. 265, k, I) in the deeper parts of 



le medulla oblongata. 

 The decmsation of the pyramids (fig. 263, 6) occupies the anterior Decussatiou 



ssure of the medulla oblongata at a distance of three-quarters of an of w ramida 

 inch below the pons. It is about a quarter of an inch in length, and 

 is generally constructed by the crossing of three or four bundles of 

 fibres from each side, but the proportion of the pyramidal fibres varies in 

 which decussate in the medulla varies much in different individuals. ex 



Dissection. For the purpose of seeing the deeper fibres of the Dissection, 

 medulla oblongata, the pyramid may be cut across on the right side 

 just below the olivary body (fig. 264) aud raised towards the pons. 



