588 COMPARATIVE PHYSIOLOGY. 



joining the vagus seems to supply a large part of the motor 

 fibers of that nerve. 



Pathological. — ^Tonic contraction of the flexors of the head 

 causes wry-neck, and when they are paralyzed the head is drawn 

 to the soimd side. 



The Hypoglossal or Twelfth Nerve.— It arises from the low- 

 est part of the calamus scriptorius and perhaps from the olivary 

 body. The manner of its emergence between the anterior pyra- 

 mid and the olivary body, on a line with the anterior spinal 

 roots, suggests that it corresponds to the latter ; the more so as 

 it is motor in function, though also containing some vaso-motor 

 fibers, in all probability destined for the tongue. ' Such sensory 

 fibers as it may contain are derived from other sources (vagus, 

 trigeminus). It supplies motor fibers to the tongue and the 

 muscles, attached to the hyoid bone. 



Pathological. — ^Unilateral section of the nerve gives rise to 

 a corresponding lingual paralysis, so that when the tongue is 

 protruded it points to the injured side ; when being drawn in, 

 the reverse. Speech, singing, deglutition, and taste may also 

 be abnormal, owing to the subject being unable to make the 

 usual co-ordinated movements of the tongue essential for these 



RELATIONS OF THE OEREBRO-SPINAL AND SYMPA- 

 THETIC SYSTEMS. 



No division of the nervous system has been so unsatisfac- 

 tory, because so out of relation with other parts, as the sympa- 

 thetic. It was also desirable to attempt to co-ordinate the cere- 

 bral and spinal nerves in a better fashion ; and various attempts 

 in that direction have been made. Very recently a plan, by 

 which the whole of the nerves issuing from the brain and cord 

 may be brought into a unity of conception, has been proposed ; 

 and, though it would be premature to pronounce definitely as 

 yet upon the scheme, yet it does seem to be worth while to lay 

 it before the student, as at all events better than the isolation 

 implied in the three divisions of the nerves which has been 

 taught hitherto. 



Instead of the classification of nerves into efferent and affer- 

 ent, connected with the anterior and the posterior horns of the 

 gray matter of the spinal cord, another division has been pro- 

 posed, viz., a division of nerve-fibers and their centers of origin 



