TRANSITION OF MEDULLA OBLONGATA INTO SPINAL CORD. 525 



the translation of the remote medullary masses of the cere- 

 bellar peduncle, continue to run undisturbed into the inner por- 

 tions of the anterior cornua of the spinal cord. Below the 

 level of the internal accessory olivary bodies this mass gives 

 off no longer hypoglossal roots, but anterior roots of the first 

 pair of cervical nerves (Stilling). The processus lateralis of 

 the anterior cornu is likewise already present (as the anterior 

 tract of origin of the lateral system of roots) in the medulla 

 oblongata. In the progressively diminishing diameter of the 

 descending central peduncle it however no. longer finds space 

 for an independent course so remote from the anterior cornu, 

 and consequently fuses with this at the level of the inferior 

 roots of the accessory nerve. 



On the other hand, the posterior cornu already appears in 

 the medulla oblongata as a continuous and circumscribed mass. 



In the spinal cord it consists of the caput ; of the cervix, 

 which is essentially composed of the traversing posterior nerve 

 roots; and of the triangular base, which is fused with the 

 remaining nuclear portion of the spinal cord, and which Goll 

 has designated the cervical triangle of the posterior cornu. 

 The nucleus of the vagus, the anterior external angle of the 

 grey matter, corresponds exactly to this cervical triangle. If 

 we now take into consideration that the caput of the posterior 

 cornu is already present in the medulla oblongata as the 

 gelatinous substance which envelopes the ascending roots of 

 the fifth, and that this is subsequently traversed by the roots 

 of the vagus entering at the apex of the triangle, which 

 is prolonged towards them (vagal nucleus), the vagal roots 

 between the above-named caput of the posterior cornu and the 

 latter mass as its base will represent the cervix of the posterior 

 cornu. This completed posterior cornu of the medulla ob- 

 longata is only turned forwards instead . of, as in the spinal 

 cord, backwards and outwards. 



If now the vagus, after coalescing with its nucleus, like this 

 nucleus, turns inwards, the gelatinous substance (G) must be 

 displaced backwards, and the whole formation of the posterior 

 cornu assume gradually a transverse position, as obviously 

 occurs in the region of the lower half of the medulla oblongata 

 in regard to the posterior roots replacing the vagus. (Fig. 261, 



