108 HAND-BOOK OF PHYSIOLOGY. 



of the medulla is a continuation of that in the spinal cord, but the ar- 

 rangement is somewhat different. 



The displacement of the anterior cornu takes place because of the 

 decussation of a large part of the fibres of the lateral columns in the 

 anterior pyramids passing through the grey matter of the anterior cornu, 

 so that the caput cornu is cut off from the rest of the grey matter, and is, 

 moreover, pushed backward by the olivary body, to be mentioned below. 

 It lies in the lateral portion of the medulla, and exists for a time as the 

 nucleus lateralis (Fig. 324, n.l)\ it consists of a reticulum of grey matter, 

 containing ganglion cells intersected by white nerve fibres. The base of 

 the anterior cornu is pushed more from the anterior surface, and when 



a:m.f. fa. P? 



FIG. 324. Section of the medulla oblongata in the region of the superior pyramidal decussation. 

 a.m./., anterior median fissure; /.a., superficial arciform fibres emerging from the fissure; ?/., 

 pyramid; n.a.r., nuclei of arciform fibres; /.a 1 , deep arciform becoming superficial: o., lower end of 

 olivary nucleus; n.L, nucleus lateralis; f.r., formatio reticularis: /.a 2 , arciform fibres proceeding 

 from the formatio reticularis; <;., substantia gelatinosa of Rolando; a. F., ascending root of fifth 

 nerve; n.c., nucleus cuneatus; n.c'., external cuneate nucleus; n.g., nucleus gracilis; f.g., nucleus 

 gracilis; .m./., posterior median fissure; c.c., central canal surrounded by grey matter, in which 

 are n.XL, nucleus of the spinal accessory, and n.XIL, nucleus of the hypoglossal; s.d., superior 

 pyramidal decussation. (Schwalbe.) (Modified from Quain.) 



the central canal opens out into the fourth ventricle, forms a collection of 

 ganglion cells, producing the eminence of the fasciculus teres; from cer- 

 tain large cells in it arise the hypoglossal nerve (Fig. 325, XII.}, which 

 passes through the medulla, and appears between the olivary body and 

 the anterior pyramids. 



In the funiculus teres, nearer to the middle line as well as to the sur- 

 face, is a collection of nerve cells called the nucleus of that funiculus (Fig. 

 325, n.t). The grey matter of the posterior cornu is displaced somewhat 

 by bands of fibres passing through it. The caput cornu appears at the 

 surface as the funiculus of Rolando, whilst the cervix cornu is broken up 

 into a reticulated structure which is displaced laterally, similar in struc- 

 ture to the nucleus lateralis. From the increase of the base of the posterior 

 cornu, the nuclei of the funiculus gracilis and funiculus cuneatus are de- 



