562 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



voluntary, or possess both volitional and involitional characteristics; some are 

 peculiar to certain species, etc. Among such movements are coughing, hawking, 

 sneezing, laughing, crying, sobbing, sighing, yawning, snoring, gargling, hic- 

 cough, neighing, braying, growling, etc. 



In coughing a preliminary inspiration is followed by an expiration which is 

 frequently interrupted, the glottis being partially closed at the time of the 

 occurrence of each interruption, so that a series of characteristic sounds are 

 caused. The air is forcibly ejected through the mouth, and thus foreign parti- 

 cles, such as mucus in the respiratory passages, may be expelled. Coughing 

 may be either voluntary or reflex. 



Hawking is somewhat similar to coughing. The glottis is, however, open 

 during the expiratory act, and the expiration is continuous. The current of 

 air is forced through the contracted passage between the root of the tongue 

 and the soft palate. Hawking is a voluntary act. 



In sneezing a deep inspiration is followed by a forcible expiratory blast 

 directed through the nose; the glottis is open, and should the oral passage be 

 open, which is not usually the case, a portion of the blast is forced through the 

 mouth. Sneezing is usually a reflex act commonly excited by irritation of the 

 fibres of the nasal branches of the fifth pair of cranial nerves. Peculiar sen- 

 sations in the nose give us a premonition of sneezing; at such a time the act 

 may be prevented by firmly pressing the finger upon the upper lip. 



In laughing there is an inspiration followed, as in coughing, by a repeatedly- 

 interrupted expiration during which the glottis is open and the vocal cords are 

 thrown into vibration with each expiratoiy movement. The expirations are 

 not as forcible as in coughing, the mouth is wide open, and the face has a 

 characteristic expression due to the contraction of the muscles of expression. 



Crying bears a close relationship to laughing so much so that at times it 

 is impossible to distinguish between the two ; hence one may readily pass into 

 the other, as frequently occurs in cases of hysteria and in young children. 

 The chief differences between the two are in the rhythm and the facial expres- 

 sion. A secretion of tears is an accompaniment of crying, but not so of 

 laughing, except during very hearty laughter. Crying normally is involun- 

 tary; laughing may be either voluntary or involuntary. 



Sobbing, which is apt to follow a long period of crying, is characterized as 

 being a series of spasmodic inspirations during each of which the glottis is 

 partially closed, and the series is followed by a long, quiet expiration. This is 

 usually involuntary, but may sometimes be arrested volitionally. In sighing 

 there is a long inspiration attended by a peculiar plaintive sound. The mouth 

 may be either closed or partially open. Sighing is usually voluntary. 



Yawning has certain features like the preceding. There occurs a long, 

 deep inspiration during which the mouth is stretched wide open, and there is 

 usually a simultaneous strong contraction of certain of the muscles of the 

 shoulders and the back ; the glottis is wide open, and inspiration is accompa- 

 nied by a peculiar sound ; expiration is short. Yawning may be either volun- 

 tary or involuntary. 



