THE PONS FINAL KEV1EW. 



217 



ease of the pons, or tumors, etc., located in front of the pons, which impinge upon 

 the peripheral portion of the cranial nerves and upon the pyramids. Inas- 

 much as the nuclei of the abducens and trigeminus are also located iu the pons, 

 these nerves may cause manifold modifications in the symptom-complex present 

 in cases of alternating paralysis originating in disease of that part. How the 

 acoustic nerve would be affected in such a case is still uncertain. 



Through the pons, also, pass all the fibres to the nerve-nuclei of the ob* 

 longata, which supply the muscles of speech. Thus, in diseases of the pons and 

 oblougata, we see disturbances of articulation, in spite of undiminished power of 

 utterance. We call this either dysarthria or anarthria, according to the degree in 

 which it is present. 



Diseases of the pons may also lead to sensory disturbances. If it is located 

 in the outer region, in the vicinity of the fillet, and is unilateral, we shall have 

 heniiauivsthesia of the opposite side. 



^- 1 ^ipy^pim.;^ 



O? Bl.TX.. 

 FIG. 132. 



The Situation of the cranial nerves. The medulla oblongata and the pons represented 



as transparent. 



Still, the sense of taste (trigeminus) and that of hearing are almost always 

 Unimpaired, and the same may be said of the sense of sight. It is usually but 

 little injured (paralysis of abducens, etc.). The picture presented by intra-poutine 

 heniiangesthesia, therefore, differs markedly from that produced by disease in the. 

 cerebrum. Bilateral heniiansesthesia may be caused by a disease situated in t he 

 middle line (inter-olivary layer). The occasional appearance of partial, direct, 

 and alternating anaesthesias of the face is explained by the situation of the 

 trigeminal nucleus. 



Disturbances of mastication ana deglutition may be observed also, because 

 the motor nuclei of the trigeminus, the glosso-pharyngeal, and the hypoglossal 

 may easily be affected by the same disease. 



It is often difficult to decide whether a disease is seated in the medulla or 

 the pons. From the situation of the motor nuclei of the vagus, accessory and 

 glosso-pharyngeal nerves such symptoms as hoarseness, loss of voice, and respir- 

 atory disturbances are usually only observed in diseases of the oblongata. Dis- 

 turbances of articulation, dysarthria, and anarthria (nucleus of hypoglossal), and 



