THE NERVOUS SYSTEM. 149 



and small intestine, and to the larynx, trachea, bronchi and lung; sensory 

 and in part vaso-motor influence to the same regions; inhibitory influence 

 to the heart; inhibitory afferent impulses to the vaso-motor centre; excito- 

 secretory to the salivary glands; excito-motor in coughing, vomiting, etc. 



Effects of Section. Division of both vagi, or of both their recur- 

 rent branches, is often very quickly fatal in young animals; but in old 

 animals the division of the recurrent nerve is not generally fatal, and 

 that of both the vagi is not always fatal, and, when it is so, death ensues 

 slowly. This difference is, probably, because the yielding of the carti- 

 lages of the larynx in young animals permits the glottis to be closed by the 

 atmospheric pressure in inspiration, and they are thus quickly suffocated 

 unless tracheotomy be performed. In old animals, the rigidity and 

 prominence of the arytenoid cartilages prevent the glottis from being 

 completely closed by the atmospheric pressure; even when all the muscles 

 are paralyzed, a portion at its posterior part remains open, and through 

 this the animal continues to breathe. 



In the case of slower death, after division of both the vagi, the lungs 

 are commonly found gorged with blood, oedematous, or nearly solid, with 

 a kind of low pneumonia, and with their bronchial tubes full of frothy 

 bloody fluid and mucus, changes to which, in general, the death may be 

 proximately ascribed. These changes are due, perhaps in part, to the 

 influence which the nerves exercise on the movements of the air-cells and 

 bronchi; yet, since they are not always produced in one lung when its 

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

 organic nervous influence. Rather, 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. 126, Vol. I.), Arteries (p. 154, Vol. I.), Salivary 

 Gland (p. 232, Vol. I.), Glottis and Larynx (p. 202, Vol. I.), Trachea and 

 Bronchi (p. 183, Vol. I.), Lungs (p. 202, Vol. I.), Pharynx and (Esophagus 

 (p. 239, Vol. I.), Stomach (p. 252, Vol. I.). 



SPINAL ACCESSORY NERVE. 



The principal branch of the accessory nerve, its external branch, sup- 

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

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

 probable that the accessory nerve gives some motor filaments to the vagus. 



