290 VARIOUS MOVEMENTS CONNECTED WITH RESPIRATION. 
strongly, and which has prevented our feeling the insufficiency 
of the ordinary respiratory movements. Hence this action is 
only occasionally connected with mental emotion. Yawning 
is a still deeper inspiration, which is accompanied by a kind 
of spasmodic contraction of the muscles of the jaw, and also 
hy a very great elevation of the ribs, in which the shoulders 
and arms partake. The purely involuntary character of this 
movement is sometimes seen in a remarkable manner in cases 
of palsy, in which the patient cannot raise his shoulder hy an 
effort of the will, but does so in the act of yawning. Never¬ 
theless the action may be performed by the will, though not 
completely; and it is one that is particularly excited by an 
involuntary tendency to imitation, as every one must have 
experienced who has ever been in company with a set of 
yawners. Sobbing is the consequence of a series of short 
convulsive contractions of the diaphragm ; and it is usually 
accompanied by a closure of the glottis, so that no air really 
enters. In Hiccup , the same convulsive inspiratory movement 
occurs, the glottis closing suddenly in the midst of it; and 
the sound is occasioned by the impulse of the column ol 
air in motion against the glottis. In Laughing , a precisely 
reverse action takes place; the muscles of expiration are in 
convulsive movement, more or less violent, and send out the 
breath in a series of jerks, the glottis being open. This some¬ 
times goes on until the diaphragm is more arched, and the 
chest more completely emptied of air, than it could be by an 
ordinary movement of expiration. The act of Crying , though 
occasioned by a contrary emotion, is, so far as the respiration 
is concerned, very nearly the same. We all know the effect 
of mixed emotions in producing something “ between a laugh 
and a cry.” 
342. The purposes of the acts of coughing and sneezing are, 
in both instances, to expel substances from the air-passages, 
which are sources of irritation there ; and this is accomplished 
in both by a violent expiratory effort, which sends forth a 
blast of air from the lungs .—Coughing occurs when the source 
of irritation is situated at the back of the mouth, in the 
trachea, or bronchial tubes. The irritation may be produced 
by acrid vapours, or by liquids or solids that have found 
their way into these passages, or by secretions which have 
been poured into them in unusual quantity as the result of 
