GRAY SUBSTANCE OF MEDULLA. 187 



Remains of gray matter of the spinal cord. At the lower part of the 

 medulla the central gray matter resembles that in the spinal cord (see fig. 

 120), but it undergoes the following changes :* The posterior cornu in- 

 creases in bulk, and extends towards the side of the cord, where it appears 

 on the surface, in front of the restiform body, as the gray tubercle of Ro- 

 lando (tuberculo cinero) (fig. 58, ). Higher in the medulla it becomes 

 the chief nucleus of the sensory root of the fifth nerve. 



The piece of the gray commissure behind the central canal of the cord 

 joins, above, the nucleus of the vagus nerve, and contributes to the audi- 

 tory nucleus : and the piece in front of the canal is laid bare in the floor 



TRANSVERSE SECTION op THE MEDULLA OBLONGATA ABOVE THE MIDDLE OF THE OLIVARY BOOT 



(Clarke). 



a. Anterior pyramid. k. Accessory olivary nucleus. 



b and c. Lateral column. I. Other gray deposits inside the olivary body. 



d. Restiform body. n. Floor of the fourth ventricle covered by 



e. Posterior pyramid. epithelium. 



/. Corpus olivare with roots of the ninth nerve o. Nnclei of the ninth nerve. 



piercing it. p. Nuclei of the vagus and glosso-pharyngeal 



g. Olivary commissure nerves. 



h. Deep transverse or commissural fibres of r. Nucleus of the auditory nerve, 

 the medulla meeting in the raph6 (a few s. Superficial transverse fibres, 

 more are added in this cut from a second t. Remains of the gelatinous substance (tuber- 

 drawing), culo ciuereo). 



of the fourth ventricle by the inclination outwards of the restiform bodies ; 

 it disappears above the fasciculi teretes. 



Special deposits of gray matter. Other masses of gray substances are 

 deposited in the medulla, both in front and behind : those behind are near 

 the floor of the fourth ventricle, and serve as nuclei of origin for certain 

 nerves ; whilst those in front are interspersed amongst the fibres continued 

 from the lateral columns of the cord. 



Nuclei at the back of the medulla. A nucleus for the hypoglossal nerre 

 is deposited in front of the central canal, and extends upwards into the 

 floor of the fourth ventricle close to the median sulcus (fig. 58, o). 



The nucleus of the accessory part of the spinal accessory nerve is placed 

 opposite that of the hypoglossal, behind the central canal. 



The nucleus of the vagus begins on a level with the fourth ventricle 



1 The description of the arrangement of the gray matter in the mednlla oblon- 

 gata is a summary of the facts contained in Mr. Clarke's paper in the "Transac- 

 tions of the Royal Society for 1858." 



