214: DISEASES OF THE BRAIX. 



we should make it a rule to ask at once whether the attacks come on 

 during rest, or only during walking, rising, etc. ; if the latter points 

 be answered affirmatively, we have obtained an important diagnostic 

 point. The dizziness observed in diseases encroaching on the posterior 

 cranial fossa depend, as Immermann has fully proved, on actual move- 

 ments of the body, which the patient does not perfectly perceive, but 

 which only have a general influence on his feeling of equilibrium. In 

 healthy persons, vibratory movements of the body would also occur in 

 walking, rising, etc., if they were not prevented by contraction of the 

 muscles which straighten and curve the spinal column. "When a 

 person is walking stiffly and uprightly, we may readily see, by the in- 

 creased prominence of the bellies of these muscles, that he is uncon- 

 sciously using them. This facility of limiting, by muscular action, the 

 movements and vibrations conveyed to the trunk is very much im- 

 paired in persons with disease encroaching on the posterior cranial 

 cavity, a circumstance which is apparently supported by the supposi 

 tion that the cerebellum chiefly causes innervation of the body, and is 

 the prop of the spinal column ( Griesinger). The diminution of sensi- 

 bility and that of motor power, which render the patient awkward and 

 uncertain, without increasing to complete paralysis and anaesthesia, are 

 simply explained by the fact that the nerve-filaments, passing from the 

 cerebrum through the foramen occipitale superius, enter the posterior 

 cranial fossa, again leave it by the interior occipital foramen, and are 

 thus subjected to a compression which impairs the propagation of ex 

 citement from the brain to the motor nerves, and of peripheral excite- 

 ment of the sensory nerves to the brain. In the disturbance of speech 

 it may be readily seen that it does not depend on lack of thoughts, or 

 on the impossibility of finding words for the thoughts, but on the un- 

 certainty and clumsiness in executing the movements necessary for 

 distinct, rapid, and connected articulation. The disturbance of deglu- 

 tition is occasionally designated as difficulty of swallowing ; it usually 

 manifests itself by slight choking while drinking. I shall not attempt 

 to decide whether this disturbance of articulation and deglutition de- 

 pends on disturbance of the function of the hypoglossal and glosso- 

 pharyngeal nerves at their origin, or in the nerves themselves, by dis- 

 eases affecting the space in the posterior cranial fossa. Besides the 

 above-mentioned symptoms, there are usually others depending on the 

 injury of certain nerves, and, if the orifice of the venae Galeni into the 

 straight sinus be compressed, and the escape of blood from the ventri- 

 cle prevented, we have the symptoms of chronic hydrocephalus. We 

 shall hereafter speak of this when treating of tumors and abscesses of 

 the cerebellum, pons, medulla oblongata, and of chronic hydrocepha- 

 lus. Here will be the place to mention those symptoms which are 



