774 EEPORT — 1887. 



a cylinder axis. To a certain extent — namely, in tlie district of the rhomboid 

 sinus — there is at the end of the iirst month a well-pronounced separation between 

 the ventral and the dorsal half of the tube, the latter being of pentagonal shape, 

 and its roof being formed by a very thin layer of cells. 



All motor fibres of the brain, from the hypoglosse to the oculomotoi-, issue 

 from cells of the ventral half of the brain tube, and there is in this point a perfect 

 correspondence with the spinal cord. 



As far as the inferior end of the rhomboid sinus the continuity of motor- 

 fibrogenous cells is preserved ; further upward these cells form certain groups, 

 partly separated by cells that do not form motor roots. We have in this way the 

 different motor centres of the 7th, 6th, 5th, 4th, and 3rd nerves. 



The path that motor fibres follow in going out are more varied in the brain 

 than in the spinal cord. Besides the accessory nerve of Willis all motor fibres of 

 the spinal cord go out from the ventral side of the organ. In the superior part of 

 the spinal cord many of the motor fibres run laterally to form the accessory nerve 

 of Willis, and the same will be found in the lower part of the brain. 



There is a long double row of fibres coming out; one of these rows is given 

 by the roots of the hypoglosse, the other by those of the nerve of Willis. The 

 mner separation of the nuclei in the motor territory is at this time not distinct. 

 Hypoglossal fibres come from the more ventral, Willis's fibres from the more dorsal 

 cells of this territory. 



Going upwards, there are in the way of the hypoglosse only two nerves, the 

 sixth and the third. In the course of the nerve of Willis we find the motor 

 fibres of pneumogastric, glossopharyngeus, facial, and fifth nerve. But we find 

 also more peculiar courses of the interior motor fibres. The fibres of the fourth 

 nerve, coming out from a venti-al nucleus, are going to the roof of tlie tube, and 

 they cross each other. The fibres of tlie facial nerve, coming from a nucleus be- 

 hind the auditory vesicle, form an interior arch before they reach tlie surface, 

 and they come out only in front of the auditory vesicle. 



The sensitive nerves and also the auditory nerve grow out of the ganglions. 

 The cells of these organs become bipolar, and every one of them sends out two 

 fibres, one going to the centre, one to the periphery. The central fibres coming 

 to the spinal cord form generally a longitudinal bundle, the first beginning of the 

 posterior column. A certain number of them go more or less directly between 

 the cells of the spinal cord. 



In the head, as is well known, four ganglion-masses are formed. Two of 

 them, the ganglions of pneumogastric and of glossopharyngeus, are behind — two 

 others, the facial-auditory and the trigeminus ganglion, in front of the auditory 

 vesicle. These ganglion-masses send out fibres also to the periphery and to the 

 brain. Besides the auditory nerve that spreads itself out near the point of its 

 entry the four other nerves come to the surface of the brain. They change the 

 direction of their fibres, and form in this way longitudinal bundles. The bundles 

 are the origins of the ascending roots of the pneumogastric, the glossopharjngeus, 

 and the fifth nerve. An ascending root of the facial nerve, or, more correctly, of 

 the nerve of Wrisberg, has also been discovered in the brain of man by the most 

 subtil investigations of Mr. Sapolini. All these ascending roots are in their 

 first origin very short, and they grow by degrees longer and longer. Then- 

 position is at first very superficial ; afterwards they become deeper by a series of 

 foldings of the brain-wall. 



The nerve-bundles formed by the motor and the sensory roots pass to the 

 periphery. Every one of them is formed by fine fibres without nuclei, some 

 connective cells being intermixed with them. The bundles <.re at first short and 

 comparatively very thick. They grow by degrees, and some weeks pass before 

 their last ends reach the periphery. 



These first new trunks go straight in the direction in which they grow out, 

 and when there is no obstacle they run a long way in a straight course. This 

 is very conspicuous in the difterent nerves of the head, in the three muscular 

 nerves of the eye, in the branches of the fifth nerve, and also in the pneumo- 

 gastric nerve, which is going with its principal branch behind the brachial arches 



