FINAL REVIEW. 405 



glosso-pharyngeal nuclei, hoarseness, aphonia, and respiratory troubles are observed 

 principally only in lesions of the oblongata. Speech-difficulties— dysarthria, an- 

 arthria (nucleus nervi hypoglossi) — and circulatory disturbances occur also more 

 often in afl'ections of the oblongata. 



Nearly all those symptoms can, in rare eases, be caused by troubles of the 

 cerebrum, since lesion of the central course of the cranial nerve-fibers leads to paraly- 

 sis the same as that of the nuclei or the peripheral nerves themselves. Paralysis of 

 the various muscles supplied by nerves from the bulb can only Avith certainty be 

 referred to a lesion in the oblongata, when accompanied by muscular atrophy and 

 when destruction of the respective nerve-trunk after its exit from the central axis 

 can be excluded. 



In the presence of cases which, through a combination of symptoms, — partici- 

 pation of widely-spread tracts and only certain cranial nerves, alternating sensory 

 or motor symptoms, — suggest that the lesion must be in the oblongata or the pons, 

 it will be serviceable to study the illustrations given above, to determine whether 

 there is any place whose destruction might cause all the symptoms. In this way it 

 will be possible in many cases to determine fairly exactly the location and size of 

 the lesion. It should not be forgotten, however, to consider the basal aspect of the 

 brain, as there disease-processes may produce pressure on the longer tracts as well as 

 destruction of the nerve-trunks. 



With this we have practically finished our task. A large number of im- 

 portant fiber-systems have been studied in their relations to the central gray 

 masses, and in their course from the cerebrum to near the end of the mid- 

 brain, or from the spinal cord upward to abo-ut that point. But it may be 

 of assistance to consider certain ones again briefly in their interrelationships, 

 because they are of particular interest physiologically and pathologically, or 

 because the general view of their relations to each other was impeded by the 

 interruption, after Chapter XX, of the series of investigation, due to didactic 

 interests. 



The following is, then, in the nature of a repetition: a short representa- 

 tion to be used with the illustrations: — 



1. The motor nerves are the continuations of the axis-cylinders of the 

 great ganglion-cells in the motor nuclei of the spinal cord and brain. 

 Around these ganglion-cells arborize the terminals of the central motor 

 paths. These run, at least to a large extent, in the pyramidal tracts. 



2. The pyramidal tracts, the most important of the motor paths, arise 

 from the upper two-thirds of the central convolutions and the paracentral 

 lobule and extend downward to a place just behind the knee of the internal 

 capsule. From there they enter the pes cerebri, occupying its middle third. 

 Below this, in the pons, their fibers are but little separated by transverse 

 fibers. When they emerge from the pons their fibers form two large bundles 

 in the ventral portion of the medulla oblongata. So they descend to the 

 spinal cord, where the larger portion of their fibers crosses over to the lateral 

 column, while a smaller portion (anterior pyramid) remains on the same side. 

 Both tracts enter into relationship with the cells of the anterior horn of the 



