IOJ2 



HUMAN ANATOMY. 



FIG. 925. 

 Dorsal 



Ventral 



Dorso-lateral aspect of inferior olivary 

 nucleus as reconstructed by Dr. Florence 

 R. Sabin. X 5. 



matter, the inferior olivary nucleus (nucleus olivaris inferior), which in favorable 

 transverse sections appears as a conspicuous sinuous C-like figure. The nucleus 

 resembles a greatly crumpled bag, of which the closed end lies beneath the 

 corresponding superficial protuberance and the mouth, or hilum, looks mesially 



and somewhat dorsally. When reconstructed and 

 viewed from the side (Fig. 925), the plications of 

 the lateral and dorso-lateral surfaces display a 

 general antero-lateral disposition. On the ventral 

 surface the grooves radiate from the ventral border 

 of the hilum (Sabin). The greatest length of the 

 inferior olivary nucleus is from 12-15 mm., its 

 transverse diameter is about 6 mm., and its vertical 

 one about one millimeter less. The somewhat 

 compressed hilum measures sagittally from 89 mm. 

 The plicated lamina of gray matter composing the 

 wall of the sac is from .2-. 3 mm. in thickness 

 and contains numerous small irregularly spherical 

 nerve-cells, each provided with a variable number 

 of dendrites and an axone, embedded within a 

 compact feltwork of neuroglia fibres. The interior of the gray sac is filled with 

 white matter consisting of nerve-fibres that, for the most part, stream through the 

 hilum and thus constitute the olivary peduncle. These strands, known as the 

 cerebello -olivary fibres, connect the cerebellar cortex with the inferior olivary 

 nucleus and probably pass in both directions. Many fibres, the axones of the olivary 

 neurones, issue from the hilum on the one side, cross the mid-line and, sweeping 

 through the opposite olivary nucleus either by way of the hilum or directly traversing 

 the gray lamina, continue their course to the restiform body and thence to the 

 cerebellum. Other fibres originate in the cells of the cerebellar cortex and proceed 

 in the opposite direction along the same pathway to end in relation with the cells 

 of the inferior olivary nucleus. The further links in the chain of conduction are 

 uncertain ; according 

 to Kolliker it is prob- FlG - 926. 



able that from some of *s2 



the olivary cells, fibres 

 pass downward into the 

 antero-lateral ground- 

 bundle of the cord. 



The accessory 

 olivary nuclei are 

 two irregular plate-like 

 masses of gray matter 

 that lie respectively 

 mesially and dorsally 

 to the chief olive. The 

 first of these, the mesial 

 accessory olivary nu- 

 cleus ( nucleus olivaris 

 accessorins mesialis) 

 -^agittally placed 

 lamina, from 10-1 I mm. 

 length, which lies 





** 



; * 



'%m 



in 



matter 



Core of 



\vhitc 

 ni.ttu-r 



between the tract of the 

 fillet and the root ti lues 

 of the hypoglossal 

 nerve. It extends be- 

 low the inferior olive 

 and, therefore, is encountered in transverse sections at a lower level immediately 

 above the pyramidal decussation than the main nucleus. According to the recon- 

 structions of Sabin, the nucleus comprises three dorso-ventral columns of cells, of 



Section of inferior olivarv nucleus, showing plicated sheet of gray substance 

 traversed by strands of cerebi-llo-olivary fibres. X 100. 



