544 HANDBOOK OF PHYSIOLOGY. 



nerve is divided, they cannot be ascribed wholly to the suspension of 

 organic nervous influence. Kather, they may be ascribed to the hindrance 

 to the passage of blood through the lungs, in consequence of the dimin- 

 ished supply of air and the excess of carbonic acid in the air-cells and in 

 the pulmonary capillaries; in part, perhaps, to paralysis of the blood- 

 vessels, leading to congestion; and in part, also, they appear due to the 

 passage of food and of the various secretions of the mouth and fauces 

 through the glottis, which, being deprived of its sensibility, is no longer 

 stimulated or closed in consequence of their contact. 



References to other functions of Vagi. Regarding the influence 

 of the vagus, see also Heart (p. 131), Arteries (p. 149 1, Salivary Gland 

 (p. 237), Glottis and Larynx (p. 440), Respiration (p. 197), Pharynx and 

 (Esophagus (p. 245), Stomach (p. 256). 



The Eleventh or Spinal Accessory Nerve. 



Origin and Connections. The nerve arises by two distinct origins 

 one from a centre in the floor of the 4th ventricle, partly but chiefly in 

 the medulla, and connected with the vagus nucleus; the other, from the 

 outer side of the anterior corner of the spinal cord as low down as the 

 5th or 6th cervical vertebra. The fibres from the two origins come to- 

 gether at the jugular foramen, but separate again into two branches, the 

 inner of which, arising from the medulla, joins the vagus, to which it 

 supplies its motor fibres, consisting of small medullated or visceral nerve- 

 fibres, whilst the outer consisting of large medullated fibres, supplies the 

 trapezius and sterno-mastoid muscles. The small-fibred branch probably 

 arises from a nucleus which corresponds to the posterior vesicular column 

 of Clarke. 



The principal branch of the accessory nerve, its external branch, then 

 supplies the sterno-mastoid and trapezius muscles; and, though pain is 

 produced by irritating it, is composed almost exclusively of motor fibres. 

 The internal branch accessory nerve supplies chiefly viscero-motor fila- 

 ments to the vagus. The muscles of the larynx, all of which, as already 

 stated, are supplied, apparently, by branches of the vagus, are said to 

 derive their motor nerves from the accessory; and (which is a very sig- 

 nificant fact) Vrolik states that in the chimpanzee the internal branch 

 of the accessory does not join the vagus at all, but goes direct to the 

 larynx. 



Among the roots of the accessory nerve, the lower or external, arising 

 from the spinal cord, appears to be composed exclusively of motor fibres, 

 and to be destined entirely to the trapezius and sterno-mastoid muscles; 

 the upper fibres, arising from the medulla oblongata, contain many 

 sensory as well as motor fibres. 



