64 GRAY SUBSTANCE OF THE TRAPEZIUM, 



which the fasciculus teres is subsequently developed, by numerous bundles of fibres, 

 along Avhich cells of medium size are frequently scattered. 



Higher up (Plate XIV, Fig. 9"), the outer border of arciform fibres has increased 

 in breadth and in the number of bundles, and reaches backwards to the upper 

 olivary bodies which are penetrated by the internal arciform fibres in a wavy course, 

 the cells being quite regularly disposed among the fibres constituting the plexus, 

 and thus becoming gradually arranged into a somewhat convoluted form. 



From this region upwards the principal changes consist in the development of a 

 still more convoluted arrangement of the cells and fibres, the cells being finally 

 separated into two or three distinct masses, forming a lamina, which, in the sheep, 

 is folded in a manner much more nearly resembling the convoluted lamina of the 

 human olivaries, than the structure of the lower olivary bodies in the medulla of 

 the same animal. In the cat, as noticed above, the structure of the lower ohvary 

 bodies approaches the human type more than in the sheep, and we find a coincident 

 development of the upper olivaries, the structure of which is quite complicated 

 (Plate XII, Fig. 42). 



Schroder van der Kolk has already pointed out the striking difi'erences which 

 exist between the diff'erent classes of mammals in the development of the upper 

 olivaries. He found the greatest development in the Carnivora, less in the Ilodentia, 

 and still less in the Herbivora; these bodies being so slightly developed in the 

 ass as to be easily overlooked. These observations are quite in accordance with 

 my OAvn; the upper olivary body in the sheep consists of two or three distinct 

 spherical bodies rather than a connected and convoluted lamina: on the other 

 hand, in the rabbit the convoluted lamina is very distinct, and often quite uninter- 

 rupted, and in the cat the convolutions are very decided (Plate XII, Fig. 42, Plate 

 IX, Fig. 36). 



In the sheep the upper olivary body consists of a mass of small cells which rarely 

 exceed ^3^3^ of an inch in diameter, varying in form from oblong or oval, to steUate; 

 they are multipolar, their processes being everywhere continuous with the numerous 

 bundles which either penetrate or radiate from the interior of the mass. The 

 olivary body is completely surrounded by fibre-bundles chiefiy radiating or turning 

 off' from the arciform plexus, many of the fibres of which penetrate the mass, form- 

 ing a somewhat similar system of fibres alternating with layers of cells, to that 

 noticed in the lower olivary bodies of the sheep. Sometimes a central bundle may 

 be noticed in the interior of the mass, from which fibres radiate in all directions, 

 but the type of structure is usually exceedingly simple. 



As the great bundles of external arciform fibres forming the trapeziwin 

 sweep down from the restiform body and posterior portion of the medulla, after 

 crossing the roots of the facial, they pursue a wavy course (Fig. 10"), in which they 

 are joined by numberless deeper lying bundles. The more external of these sweep 

 around the olivary body, many separate bundles turning off' and curving quite 

 around the mass, either penetrating its interior or completely surrounding it, tiU 

 the upper side is reached, where the bundle frequently turns still more and enters 

 the central portion of the mass, radiating in the same manner as the bundles which 

 enter the convolutions in the lamina of the human olivaries. 



