THE PONS FINAL REVIEW. 2*23 



joins the other part which had already crossed in the spinal 

 cord. The two, united, form the pyramids of the oblongata. 



We also know that the sensory nerves have an analogous 

 central course. The nerve first passes to its nucleus in the 

 spinal ganglion. From the nucleus a direct tract is developed, 

 which passes upward in the posterior columns. In the oblongata 

 it passes over to the other side. Their course differs from that 

 of the motor nerves in that they pass through a nucleus (nucleus 

 of the posterior column) before decussating. In addition to 

 this, there is given off from the spinal ganglion a tract which 

 decussates directly after entering the spinal cord, but this tract 

 must also pass through the unknown mechanism of the posterior 

 horn. 



There is an important and characteristic difference between 

 the ways in which the two sets of nerves are connected with 

 their prolongations into the brain. 



The connection is always a crossed one, but, in the case of 

 the sensory nerve, an additional apparatus is interposed in the 

 cord, between the nucleus of origin, which lies outside the cord, 

 and the central tract. With a motor nerve the case is different ; 

 its nucleus of origin already lies in the cord. 



7. The central course of the trigeminus from the cortex to 

 the capsule is unknown. Its fasciculi must, according to patho- 

 logical experience, lie in the posterior third of the capsule. 

 From here a tract must pass to the tegmental nuclei, the most 

 anterior of which lies under the corpora quadrigemina, in the 

 lateral wall of the aqueduct, the middle one in the midst of the 

 pons, and the most posterior extends from the cervical cord up 

 to the point of exit of the nerve. Near the point of exit is 

 situated the motor nucleus of the nerve. Patholo^v teaches us 



O *' 



that the ascending root contains the sensory fibres for the face. 

 The central tract reaches all these from the fillet of the opposite 

 side. These fibres are well known and were described in Lec- 

 ture XI. From the trigeminal nuclei arise the roots whose 

 sensory portions pass into ganglia (Gasserian and ciliary ganglia, 



