CEPHALIC NERVES PNEUMOQ ASTR 1C NERVE. 623 



have, of an abnormal condition of the organs which it supplies. Thus, the 

 suspension of the respiratory movements gives rise to a feeling of the greatest 

 uneasiness, which must be excited by impressions conveyed through this 

 nerve from the lungs ; and an inflamed state of the walls of the air-passages 

 causes the contact of cold and dry air to produce distressing pain and irri- 

 tation ; yet of the ordinary impressions conveyed from these organs, which 

 are concerned in producing the respiratory movements, and in regulating 

 the actions of the glottis, we are not conscious. The same may be said of 

 the portion of the nerve distributed upon the alimentary tube; for the pharyu- 

 geal branches are almost exclusively motor, the afferent function being 

 performed by the glosso-pharyngeal ; whilst the oesophageal and gastric are 

 both afferent and motor, conveying impressions which excite reflex move- 

 ments in the muscles of those parts, but which do not become sensations ex- 

 cept under extraordinary circumstances. The participation of this nerve in 

 the operations of Deglutition, Digestion, Circulation, and Respiration, and 

 the effects of injury to its trunk or branches, have already been considered 

 in the account of those functions. 1 



496. In regard to the functions of the Spinal Accessory nerve, also, there 

 has been great difference of opinion ; the peculiarity of its origin and course 

 having led to the belief, that some very especial purpose is answered by it. 

 It may be said to have three roots of origin (Lockhart Clarke) one from 

 the anterior gray substance of the Spinal Cord, a second from the nucleus 

 of the Hypoglossal nerve, and a third from the tract of vesicular substance 

 in the Medulla Oblougata, common to it and the Vagus nerve. The trunk 

 contains from 2000 to 2500 tubules. The predominance of motor fibres in 

 its roots, its inosculation with the Pneumogastric, and its probable reception 

 of sensory fibres from the latter, whilst imparting to it motor filaments, have 

 been already referred to ( 494). As its trunk passes through the foramen 

 lacerum, it divides into two branches ; of which the internal, after giving 

 off some filaments that assist in forming the pharyngeal branch of the 

 Pneumogastric, becomes incorporated with the trunk of that nerve ; whilst 

 the external proceeds outwards, and is finally distributed to the sterno- 

 mastoid 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 func- 

 tions 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, after section of the Pneumogastric Nerves ( 494), is unattended with 

 any muscular movement. Hence it is clear that the motions in the steruo- 

 mastoid and trapezius muscles, occasioned by irritating it, are of a direct, not 

 of a reflex character ; though the movements which occur in the laryngeal 

 and pharyngeal muscles, on irritation of the centric extremity, are un- 

 questionably reflex in their nature. According to Sir C. Bell, the Spinal 

 Accessory is a purely Respiratory nerve, whose office it is to excite the in- 

 voluntary or automatic movements of the muscles it supplies, which share 

 in the act of respiration ; and he states that the division of it paralyzes, as 

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



1 For a careful inquiry into the effects of section of this nerve in producing pul- 

 monary lesions, see Boddart, Journ. de la Physiologic, t. v, pp. 442 and 527. 



