MAMMALIAN. 53 



CHAPTER V. 



THE UPPER OLIVAPvY BODIEf!. 



The nuclei within the mammalian trapezium, situated anteriorly on each side of 

 the raphe, resembling in form and structure the olivary bodies of the meduUa, were 

 first pointed out by Clarke,-' and subsequently described quite fully by Schroder van 

 der Kolk.^ They make their appearance in the upper part of the medulla, at a 

 point near where the lower olivaries first diminish in size, in the situation formerly 

 occupied by the cells of the antero-lateral nucleus. The cells of this group have, 

 however, dimuaished very much in number prior to the appearance of the upper 

 olivary bodies (Plate XIII, Figs. 6", 7"), and in the cat they sometimes almost 

 entkely disappear. By comparing Plate XIII, Figs. 6", 7" with Plate XIV, Fig. 

 8", it will be seen that the upper olivary group is developed in a position exactly 

 corresponding to that of the antero-lateral nucleus below, of which it may therefore 

 be considered an upward extension, serving in the lower part of the medulla, as it 

 were, as an accessory nucleus to the lotver olivary eohnnn, and closely connected at 

 the same time with the caput cornu, as well as with the nuclei of the posterior 

 columns {glossopharyngeal, vagal and spinal accessory'). 



In the first stage of its development as an independent nucleus (Plate XIV, Fig. 

 * 8"), the upper olivary body appears as a group of large, stellate, multipolar cells, 

 measuring in the sheep from -g^g- to -^^-^ of an inch in diameter, in the cat from 

 y 3^3-3^ to -g^-g of an inch. These cells are very numerous, especially in the cat, and 

 are quite imiform in size when measured on the same plane ; in the lower part 

 of the nucleus they are quite large, but rapidly diminish in size as we approach 

 the trapezium. At first they are arranged in a loose network, formed by the 

 interlacement of their processes around the numerous longitudinal bundles of the 

 anterior network. The cell-processes appear to run in every direction, being 

 continuous before and behind with the transverse fibres radiating from the central 

 gray substance, and laterally with the arciform fibres, in addition to which other 

 processes are sent out above and below to join the longitudinal bundles. The 

 meshes formed in this way are exceedingly numerous and intricate, and the develop- 

 ment of anything like the regular convolution of a true olivary body is very gradual. 

 The mass is still connected by little cell-groups with the caput cornu, as was the 

 case with the antero-lateral nucleus, and is also joined more or less to the central 

 and anterior portion of the great auditory nucleus, especially to that portion from 



* Proceedings of the Royal Society, 1857. 

 =■ Medulla Oblongata, 162 et seq. 



