CEPHALIC NERVES. HYPOGLOSSAL NERVE. 691 



that assist in forming the pharyngeal branch of the Pneumogastric, becomes 

 incorporated with the trunk of that nerve; whilst the external proceeds out- 

 wards, and is finally distributed to the sterno-cleido-mastoideus and trapezius 

 muscles, some of its filaments inosculating with those of the cervical plexus. 

 When the external branch is irritated, before it perforates the sterno-mastoid 

 muscle, vigorous convulsive movements of that muscle and of the trapezius are 

 produced ; and the animal does not give any signs of pain, unless the nerve be 

 firmly compressed between the forceps, or be included in a tight ligature. 

 Hence it may be inferred that the functions of this nerve are chiefly motor, and 

 that its sensory filaments are few in number. Further, when the nerve has 

 been cut across, or firmly tied, irritation of the lower end is attended by the 

 same convulsive movements of the muscles; whilst irritation of the upper end, 

 in connection with the spinal cord, is unattended with any muscular movement. 

 Hence it is clear that the motions occasioned by irritating it are of a direct, not 

 of a reflex character. The same muscular movements are observed on irritat- 

 ing the nerve in the recently-killed animal, as during life. According to Sir 

 C. Bell, the Spinal Accessory is a purely Respiratory nerve, whose office it is to 

 excite the involuntary or automatic movements of the muscles it supplies, which 

 share in the act of respiration; and he states that the division of it para- 

 lyzes, as muscles of respiration, the muscles to which it is distributed; though 

 they still perform the voluntary movements, through the medium of the spinal 

 nerves. Both Valentin and Dr. J. Reid, however, positively deny that this is 

 the case ; and Dr. Reid's method of experimenting was well adapted to test the 

 truth of the assertion. 1 The functions of this nerve have been made the sub- 

 ject of special examination by M. Cl. Bernard, 3 who has arrived at the conclu- 

 sion that the Spinal Accessory is a purely motor nerve, whose action is not 

 essential to the ordinary movements of respiration, these being provided for by 

 the Pneumogastric and ordinary Spinal nerves; but that its special function is 

 to bring the respiratory movements into accordance with the requirements of 

 Animal life, adapting the actions of the muscles of the larynx and thorax to 

 the production of voice, or to general muscular effort. The internal branch, 

 which is especially distributed, with the fibres of the Pneumogastric, to the 

 pharynx and larynx, is peculiarly subservient to the former of these purposes; 

 and the external to the latter. This conclusion is sufficiently in accordance with 

 the results obtained by other experimenters, to be received as a probable expla- 

 nation of the facts which have been observed by them. 



720. The Hypoglossal nerve, or Motor Linguae, is the only one which, in the 

 regular order, now remains to be considered. That the distribution of this 

 nerve is restricted to the muscles of the tongue is a point very easily esta- 

 blished by anatomical research ; and accordingly, we find that long before the 

 time of Sir C. Bell, Willis had spoken of it as the nerve 1 of the motions of 

 articulation, whilst to the Lingual branch of the 5th pair he attributed the 

 power of exercising the sense of taste ; and he distinctly stated that the reason 

 of this organ being supplied with two nerves is its double function. The 

 inference that it is chiefly, if not entirely, a motor nerve, which has been 

 founded upon its anatomical distribution, is supported also by the nature of its 

 origin, which is usually from a single root, corresponding to the anterior root 



1 See his "Physiol., Pathol., and Anat. Researches," p. 151 ; and "Edinb. Med. and 

 Surg. Journ.," Jan., 1838. 



2 " Recherches Experimentales sur les Fonctions du Nerf Spinal," in "Archives de 

 Medecine," 1844. This memoir, having gained the prize given by the Academic des 

 Sciences for experimental physiology in 1845, has been printed in the " Recueil des Savants 

 Strangers," torn, xi., 1851 ; and the author states that since the first publication of his 

 researches, he has confirmed his original conclusions by the repetition and variation of his 

 experiments. 



