156 TEXT-BOOK OF PHYSIOLOGY. 



well as a secretor character. Unless the dose of atropin be largely increased, 

 e.g., 100 milligrams, it fails to depress the conductivity of the terminals of 

 the sympathetic nerve fibers. 



Pilocarpin. Pilocarpin in small doses, from 2 to 5 milligrams, hypo- 

 dermatically causes in the cat a free flow of saliva which may amount to half 

 a liter or more in the course of several hours. In human beings its effect on 

 the flow of saliva is equally marked. Ringer reports that in two patients, 

 after taking a medicinal dose, the amount of saliva discharged was 622 c.c. 

 and 764 c.c. respectively. Since division of the nerves both pre- and post- 

 ganglionic, does not diminish or abolish the secretion, the inference is that 

 the pilocarpin exerts a stimulating action on the nerve endings in connection 

 with the gland cells. This inference is strengthened by the fact that the 

 pilocarpin effect is antagonized and the secretion checked by a suitable dose 

 of atropin, the seat of the action of which is known. The two alkaloids thus 

 appear to be in physiologic antagonism in their action on these nerve termi- 

 nations. The action of pilocarpin is not limited to the salivary glands, but 

 extends to glands found in the alimentary canal, respiratory passages, and 

 skin. 



DEGLUTITION. 



Deglutition is -that part of the digestive process which is concerned in 

 the transference of the food from the mouth through the pharynx and 

 esophagus into the stomach. This is an extremely complex act and involves 

 the action of a large number of structures, all of which are made to act in 

 proper sequence under the coordinating influence of the nerve system. The 

 deglutitory canal consists of the mouth, pharynx, and esophagus, each of 

 which presents certain anatomic features on which its physiologic action 

 depends. 



The cavity of the mouth communicates posteriorly with the pharynx by 

 a narrow orifice, the isthmus of the fauces. This orifice is bounded above 

 by the soft palate, laterally by the anterior and posterior half arches, and 

 below by the tongue. 



The pharynx is an oval-shaped cavity extending from the base of the 

 skull to the lower border of the cricoid cartilage, a distance of about 12 centi- 

 meters. (See Fig. 72.) Its walls are formed mainly by three pairs of 

 muscles the superior, middle, and inferior constrictors each consisting 

 of red, striated muscle-fibers, and hence capable of rapid and energetic 

 contractions. Superiorly the pharynx is attached to and supported by the 

 basilar process of the occipital bone; inferiorly it becomes continuous with 

 the esophagus. The anterior wall of the pharynx is imperfect and presents 

 openings which communicate with the nasal chambers, the mouth, and the 

 larynx. The lateral wall on either side presents the opening of the Eustachian 

 tube which leads directly into the cavity of the middle ear. The interior of 

 the pharynx is lined by mucous membrane. The pharynx is partially separ- 

 ated from the mouth by the velum pendulum palati, a muscular structure 

 attached above to the hard palate; its lower edge or border is directed 

 downward and backward and presents in the middle line a conical process, 

 the uvula. On either side the palate presents two curved arches, the anterior 



