584 MANUAL OF HISTOLOGY. 



divided into two portions, namely, the crura cerebflli ad mcdullam oblonga- 

 tnm and adpontem. The pedunculi cerebrii connect it with the cerebrum. 

 Finally, numerous nervous trunks spring from the medulla oblongata. 



Turning now from this mere outline sketch to the structure as seen with 

 low magnifying powers, the full peculiarity of the medulla oblongata soon 

 strikes us. 



The cornua of the central grey mass, as found in the medulla spinalis, 

 become rapidly changed here, the alteration of shape commencing at the 

 point, of junction of anterior and posterior cornu, and spreading from 

 thence further and further. Instead, namely, of the continuous grey sub- 

 stance of another part of the cord, the cineritious matter here assumes 

 the appearance of a series of bands or network, through which nerve 

 fibres take their course (formatio reticularis). 



This metamorphosis then gradually extends, affecting eventually the 

 white columns also almost throughout the whole medulla oblongata. 



Here and there, however, masses of grey matter still remain undis- 

 turbed, which are known as the nuclei of the medulla oblongata; these 

 give rise to further peculiarities. 



Such nuclei are of two kinds. From one set of them the nerves 

 springing from the medulla oblongata seem to take their rise primarily : 

 these are the nerve nuclei of Stilling. A large number of them may be 

 recognised, as we shall see later on. They have nothing absolutely new 

 in them as compared with the spinal cord, and are equivalent to the 

 sources of origin of the spinal nerves. 



But in addition to these, we meet with collections of ganglionic matter 

 presenting other characters. These have nothing to do with the origin of 

 peripheral nervous tracts ; they seem rather to be the points at which the 

 fibres and cords of the medulla oblongata end provisionally, previous to 

 their becoming changed both as to number of fibres and direction, and 

 making their way into the brain. 



Among these specific nuclei, as we shall call them for shortness' sake, 

 may be numbered, in the first place, the inferior olives (olivary bodies, in 

 a word), with the accessory olives; then the superior olives, formerly 

 erroneously held to be an upper nucleus for the trigeminus by Stilling, and 

 a grey nucleus of considerable size imbedded in the lateral column, and 

 named by Schultze the nucleus of Deiters ; then, again, the pyramid nuclei 

 and so-called ganglia post-pyramidalia of Clarke, situated in the posterior 

 columns ; and further, the special grey masses of the pons Varolii. Taking 

 a still wider view with Deiters, we may include here the corpus dentatum 

 cerebelli, the grey collections in the interior of the crura cerebelli, as well 

 as those constituting the greater part of the corpora quadrigemina. 



The bundles of white fibres, then, ascending from the medulla spinalis, 

 although they may be found again in the medulla oblongata, preserve no 

 longer their original uniformity of direction, but pursue, in many cases, a 

 totally different course. 



Besides the latter fasciculi, there appears in the medulla oblongata 

 another very peculiar and complicated system of nerve tubes, that of the 

 transverse, arched, and circular fibres (a, a). This was named, many 

 years ago, the zonal by Arnold. In the raphe a very complex group of 

 these intersecting fibres exists, but grey matter presents itself here also. 



If, in addition to all this, we remember the root fibres of the afferent 

 and efferent nerves, we cannot but be struck with the truly labyrinthine 

 complexity of the medulla oblongata. 



