io8 THE NERVOUS SYSTEM 



BULBAR PARALYSIS. As the motor nuclei of the ninth, 

 tenth, twelfth and the cerebral portion of the eleventh are 

 intimately related to one another in the medulla oblongata (Fig. 

 52), it is not surprising to find that they may all be involved in 

 certain, slowly progressive, degenerative processes. Further, 

 as the nucleus ambiguus (p. 94) and the hypoglossal nucleus 

 represent the upward continuation of the anterior column of 

 the grey matter of the spinal medulla, the spread of the pro- 

 cess from the one to the other is of common occurrence. 



The term bulbar paralysis is applied to lesions affecting the 

 motor nuclei of the medulla oblongata, whether they occur 

 as the starting-point of a downward spreading process or in 

 the later stages of an upward spreading process, e.g. pro- 

 gressive muscular atrophy (p. 46). The symptoms vary in 

 different cases, as the disease does not attack the groups of 

 cells within the nuclei in any fixed order. 



As a rule, the hypoglossal nuclei are first involved, and 

 weakness of the tongue muscles and the orbicularis oris 

 (p. 107), causing difficulties in speech and deglutition, are 

 often the first signs that a case of progressive muscular 

 atrophy has entered on its last stage. Later, the muscles of 

 the pharynx and soft palate are involved and the patient 

 becomes unable to swallow. Paralysis of the laryngeal 

 muscles is not usually very noticeable, but, when the ary- 

 epiglottici (p. 332) are affected early there is grave danger of 

 aspiration pneumonia. 



The same symptoms may arise suddenly, owing to small 

 haemorrhages or areas of embolic softening in the medulla 

 oblongata. The distinctive term " acute bulbar paralysis " has 

 been given to this condition. 



THE MEMBRANES OF THE BRAIN 



The brain is surrounded by three membranous layers, 

 termed the dura mater, the arachnoid and the pia mater. 

 The spaces separating these membranes from one another 



