THE OLIVARY BODY. 



311 



and in front of the bottom of the fourth ventricle, lies a large 

 group of multipolar cells, the liypoglossal nucleus, from which 

 bundles of fibres course forward through the olivary body, 

 which is here much enlarged and more complex than in the 

 last section. On the inner side of the liypoglossal roots in 

 the olivary region is an elongated mass of gray matter con- 

 taining small cells, called the parolwary nucleus. There is 

 an oval group of fusiform cells at, behind, and external to 

 the hypoglossal nucleus, from which indistinct and broken 

 bands of fibres pass outward to emerge from the lateral re- 

 gion of the medulla. This constitutes the upper spinal acces- 

 sory nucleus and root. Behind this nucleus, forming the 



FIG. 136. Diajjram showing structure of 

 one fold of the olivary nucleus : C, centripe- 

 tal fibres; P, peripheral fibres, x 04. 



FIG. 137. One-half transverse section of 

 the human medulla at the point of fusion of 

 the central canal and the posterior fissure to 

 form the fourth ventricle : 11, spinal acces- 

 sory root ; 12, hypoglossal root ; B, raphe. 



eminence on each side of the fourth ventricle, is a large mass 

 of gray matter containing a great number of small nerve-cells, 

 which also seems to be rather indistinctly connected with 

 the spinal accessory root. External to this nucleus is a con- 

 tinuation of the collection of large cells seen in the section 

 lower down, the lower sensory nucleus of the fifth. In front 

 of the spinal accessory root is seen a group of multipolar cells 

 not so large as in preceding sections. The peripheral circular 

 fibres in this region are confined to the anterior and external 

 aspect of the medulla, and are still seen to be in connection 

 witli the raphe by the arcuate fibres which traverse obliquely 

 the intervening nervous tissue. 



From this point to the middle of the olives, sections differ 



