392 PHYSIOLOGY CHAP. 



peripheral end of the cut hypoglossal was sensitive, which he 

 attributed to recurrent twigs of the lingual. 



Panizza gave an exhaustive description of the effects of 

 bilateral division of the hypoglossal in dogs, all of which depend 

 on the paralysis of the tongue muscles. The animal is no longer 

 capable of lapping up liquids with its tongue, nor of swallowing 

 solids after masticating them, unless the alimentary bolus drops 

 into the pharynx passively when the head is held up. If during 

 the movements of the head and jaws the tip of the tongue projects 

 from one or other corner of the mouth it remains there, for the 

 animal is incapable of drawing it back. If the tongue is bitten 

 during mastication, the animal gives a cry of pain, showing that 

 painful sensibility is unaffected. If a drop or two of concentrated 

 solution of quinine, which has a very bitter taste but no smell, 

 is dropped on the tongue, the animal shakes its head and lips 

 violently and makes agitated movements of mastication, as if to 

 get rid of an unpleasant sensation. This proves that the sense of 

 taste is preserved. 



Electrical stimulation of the peripheral end of the divided 

 hypoglossal provokes contractions of all the muscles of the tongue, 

 except the palato-glossal and pharyngo-glossal. The fibres of the 

 three first cervical nerves, which anastomose with the hypoglossal, 

 are distributed to the thyro-hyoid and genio-hyoid muscles. 



Hypoglossal paralysis in man confirms the results of experi- 

 ments on dogs; the effects are purely motor. In bilateral 

 paralysis the tongue cannot move in the mouth ; hence there are 

 disturbances in speaking and singing, slow mastication, and great 

 difficulty in swallowing owing to the incapacity of the tongue to 

 drive the food into the pharynx ; tactile and pain sensibility are 

 unaltered, but taste is slightly blunted as the tongue cannot 

 manipulate the food. 



In unilateral hypoglossal paralysis the tongue is higher on 

 the paralysed than on the healthy side, owing to loss of tone in 

 these muscles; the tip of the tongue is deflected towards the 

 healthy side, which is somewhat shortened by the physiological 

 tone of the non-paralysed longitudinal fibres. When, on the 

 contrary, the tongue is protruded from the mouth, it is twisted 

 towards the paralysed side, owing to the one-sided action of the 

 genio-glossus, which from the direction of its fibres draws the 

 healthy half of the tongue towards the median line. In this 

 unilateral paralysis of the tongue, speech, mastication, and degluti- 

 tion are but slightly affected. 



A few months after experimental transection or paralysis of 

 one hypoglossus, the muscular atrophy of the paralysed half of the 

 tongue becomes very pronounced. 



III. Scarpa, Bischoff, and many others regarded the 10th 

 and llth nerves, i.e. the Vagus and the Spinal Accessory, as one 



