This Subject is best reached from the point of reflecting that, of all the animals, man alone appears to be capable of laughter. If, as so many naturalists now claim, man has ascended by successive evolutions of varieties from a lower animal type, we ought to be able to find some germs of the laughing propensity among our ancestors. The first witness we summon on this question is the anatomist, because the physical expression that accompanies an act of laughter depends upon the connection of the respiratory nerves with the diaphragm below and the orbicular and straight muscles of the mouth above. But these muscles are not perfectly developed in the animals. When dogs are fondly gambolling about you, there is "a slight eversion of the lips," which is a rudimentary hint of man's facial expression in an act of mirth. The dog has been the associate of human moods in all countries, and for thousands of years; yet, although we are told that "the little dog laughed to see the sport," he has not yet made up his mouth for any thing more emphatic than a simper.
Some kinds of monkeys have established a facial expression, accompanied with a laughing noise, which is
