578 



Of the corpora olivaria it is remarked, that they are to be found 

 not only in all mammalia, but also to a certain extent in birds. In 

 man, the surface of each olivary body consists of two layers of fibres 

 transverse and longitudinal ; the former in part belong to the 

 arciform system, the latter are continuous with the antero-lateral 

 column. Abroad transverse commissure unites the two bodies. The 

 corpus dentatum is a convoluted vesicular sac, consisting of nucleated 

 cells of small and rather uniform size, from y^jth to -pfVo^h ^ 

 an inch in diameter, but varying in shape, and many of them send- 

 ing out processes some one, others two, three or more. The con- 

 nexion of the fibres with the convolutions of the sac is extremely 

 complicated, and not to be made intelligible without the aid of 

 diagrams. It may be stated, however, that the fibres which are 

 confined to the cavity of the sac, with some others, take their origin 

 from the cells. 



In mammalia generally the olivary bodies are nearly concealed 

 behind the pyramids, and vary in their appearance at the surface in 

 different animals. The vesicular sac, or corpus dentatum, is thrown 

 into only a few comparatively large convolutions. On the outer side 

 of each olivary body, and separated from it by a groove which lodges 

 the hypoglossal nerve, is another vesicular column, not hitherto de- 

 scribed by anatomists, and of which the analogue is found in the 

 human medulla. 



As the fibres of the lateral columns cross over to the anterior 

 pyramids, the posterior cornua sink as it were forwards, while their 

 terminal tufts the gelatinous substance, gradually increasing in 

 bulk, reach the surface, and form the grey tubercles of Rolando. 

 At the same time, and close to the posterior median fissure, the grey 

 substance is raised into a small conical projection, from which a net- 

 work of blood-vessels and fibres extends backwards into the posterior 

 pyramid. Within the projection, and amongst the network, cells 

 are developed, which are circular, pyriform, or irregular in shape, 

 and give off one process or several. Further outwards, another, but 

 larger projection and another network extend backwards into the 

 restiform body, containing cells of the same character, but of supe- 

 rior size. These additional productions may be called respectively 

 the post-pyramidal and restiform ganglia. 



As the medulla ascends, the root of the posterior cornu and the 



