THE NERVOUS SYSTEM 



1355 



towards the median line, but it stops short of either end of the 

 nucleus. A great many nerve-fibres pass through the hilum, some 

 inwards and others outwards, and these form what is known as the 

 olivary peduncle. The wavy lamina is traversed by nerve-fibres. 



The superior olivary nucleus is situated in the dorsal or tegmental part ot 

 the pons Varolii. 



The mesial accessory and dorsal accessory olivary nuclei are situated 

 on the mesial and dorsal aspects, respectively, of the inferior or 

 chief olivary nucleus, from which, however, they are distinct. 

 Each consists of a band of grey matter, and the upper part of the 

 mesial accessory nucleus lies opposite the hilum of the chief nucleus. 



7 6 2 



L.5' 



Fig. 568.— Transverse Section passing through thb Sensory Decussation 

 (Schematic) (L. Testut's * Anatomie Humaine '). 



1. Anterior Median Fissure 



2. Posterior Median Fissure 



3, 3'. Caput and Base of Anterior Cornu 

 (in red) 

 4. Hypoglossal Nerve 

 5, 5. Caput and Base of Posterior Comu 



6. Nuclen? Gracilis 



7. Nucleus Cuneatus 



8, 8. Fillet, or Sensory Tract 

 9. Sensory Decussation 

 low Pyramidal Tract 



Structure of Inferior Olivary Nucleus. The wavy lamina consists 

 of many small nerve-cells and nerve-fibres which traverse it. The 

 axons of the nerve-cells leave the nucleus as nerve-fibres, and pass 

 to the raphe of the bulb. Some of the nerve-fibres which traverse 

 tlie wavy grey lamina terminate in connection with its cells, and 

 other fibres pass through it. 



The inferior olivary nucleus receives a tract of fibres, called the 

 thalamo-olivary tract, which descends from the optic thalamus 

 through the central part of the tegmentum. 



The structure of the two accessory^ olivarj'^ nuclei corresponds to 

 that of the chief or inferior olivary nucleus. 



Arcuate Nucleus. — ^This nucleus consists of a lamina of grey 

 matter which lies upon the ventral aspect of the pyramid of the 

 bulb, above the level of the decussation of the p^Tamids, and 



