402 COMPARATIVE PHYSIOLOGY. 



Crying is essentially the same as laughing, but the facial 

 expression is different, and the lachrymal gland functions ex- 

 cessively, though with some persons this occurs during laughter 

 also. 



Sobbing is made up of a series of inspirations, in which the 

 glottis is partially closed, followed by a deep expiration. 



Yawning involves a deep-drawn, slow inspiration, followed 

 by a more sudden expiration, with a well-known depression of 

 the lower jaw and usually stretching movements. 



Sighing is much like the preceding, though the mouth is not 

 opened widely if at all, nor do the stretching movements com- 

 monly occur. 



Hiccough is produced by a sudden inspiratory effort, though 

 fruitless, inasmuch as the glottis is suddenly closed. It is 

 spoken of as spasm of the diaphragm, and when long continued 

 is very exhaustive. 



Sneezing is the result of a powerful and sudden expiratory 

 act following a deep inspiration, the mouth being usually closed 

 by the anterior pillars of the fauces against the outgoing cur- 

 rent of ail', which then makes its exit through the nose, while 

 the glottis is forcibly opened after sudden closure. It wUl be 

 noticed that in most of these acts the glottis is momentarily 

 closed, which is never the case in mammals during quiet res- 

 piration. 



This temporary occlusion of the respiratory passages per- 

 mits of a higher intrapulmonary pressure, which is very effect- 

 ive in clearing the passages of excess of mucus, etc., when the 

 glottis is suddenly opened. Though the acts described are all 

 involuntary, they may most of them be imitated and thus 

 studied deliberately by the student. It will also appear, con- 

 sidering the many ways in which some if not all of them may 

 be brought about, that if the medullary center is responsible for 

 the initiation of them it must be accessible by numberless paths. 

 Comparative. — Few of the lower animals cough with the 

 same facility as man, while laughing is all but unknown, cry- 

 ing and sobbing rare, though the whining of dogs is allied to 

 the crying of human beings. 



Sneezing seems to be voluntary in some animals, as squir- 

 rels, when engaged in toilet operations, etc. 



Barking is voluntary, and in mechanism resembles c6ugh- 

 ing, the vocal cords being, however, more definitely employed, 

 as also in growling. 



