ORGANS OF THE BODY. 589 



spring from the cells of the forrnatio reticularis, wiiich receives fibres 

 both from the lateral and posterior cords. This explains the increase in 

 volume also supervening upon the formation of the pyramids. After 

 their decussation the latter advance into the brain through the crura cerebri, 

 strengthened by additional bundles of fibres, but augmented no farther 

 by grey matter. Here they are said to reach as far as the corpora striata, 

 nuclei dentati, and even the cortical portion of the hemispheres. 



The olivary bodies (i.e., inferior) are, as is well known, very character- 

 istic organs of the medulla oblongata. Their grey substance forms in 

 man a peculiar corrugated capsule, the corpus dentatum olivce, which 

 encloses a white nucleus on all sides except internally. In the spongy 

 sustentacular tissue of this cineritious substance we find, according to 

 Clarke and Dean, small yellowish cells from 0*0156 to 0'0189 mm. in 

 diameter with rounded body, and the so often mentioned two species 

 of processes. .Between these small bundles of the most delicate nerve- 

 filaments take their course. 



It has been supposed by many that there exists some relationship 

 between the olivary bodies and the hypoglossal nerves that they are in 

 some way "auxiliary organs" for the latter; but this is not the case. It 

 is true that the roots of these motor nerves, so remarkable for the size of 

 their fibres, pass by the organs in question, a few even through them in 

 part, but no connection with their elements takes place. 



Deiters' researches, which we here quote, have led him to the conclusion 

 that those very delicate fibres received into the olivary bodies, to termi- 

 nate provisionally in their cells, are derived, as has been already men- 

 tioned, in each case from the posterior columns, each olive obtaining, how- 

 ever, fibres from both sides of the cord. A new system of fibres then 

 springs from these cells, which passes partly into the brain, partly into the 

 cerebellum. Thus we see that the olivary bodies also belong to those 

 interpolations in the very complicated chain of the central organs, and are 

 related both to the cerebellum and pons. Besides, they are traversed by 

 numerous fibres of the circular and transverse systems. Further, they 

 are embraced round their external border by a set of zonal fibres springing 

 from the posterior columns. At the summit of the olivary bodies poste- 

 riorly, the so called accessory olivary nuclei of Stilling present themselves, 

 having a similar texture to the former, while higher still, above the abdu- 

 cens and facialis, and external to the first of these nerves, another body 

 of similar structure is to be found on each side, known as the superior 

 olive; this is not absent in man, but is buried in the pons. It likewise 

 possesses a zonal system of fibres. It was formerly supposed to be con- 

 nected with the facial or acoustic nerves of its own side. 



Let us now turn our attention for a moment to the crura or connecting 

 bands of the medulla oblongata. 



The crura cerebdli ad medidlam oUongatam are, without doubt, in part 

 processes of the latter continued into the little brain. Their fibres consist 

 for the most part of prolongations to the stratum zonale of Arnold, spring- 

 ing, in the first place, from the olivary bodies, and probably also from the 

 nucleus of Deiters in the lateral column, and from the corpus trapezoides. 

 Meinert, however, states that a sensory band from the funiculus gracilix 

 and cuneotus passes into the cerebellum, and a motor from the latter 

 downwards back into the cord again. 



The fibre bundles of the crura cerebelli ad pontem possess quite a dif- 

 ferent significance. Apart from the fact that they connect similar portions 



