298 ADDITIONAL SENSES. 



addition to those found in man. These contain the roots of the dentes 

 incisores, when such are present ; but they also exist in animals that 

 are destitute of teeth. They are termed ossa intermaxillaria, ossa 

 incisoria, and ossa labialia; and are situate, as their names import, at 

 the anterior part of the jaw, and between the ossa maxillaria or jaw 

 bones. Jacobson 1 considers them to be an organ of sense, as they 

 communicate with the exterior, and are largely supplied with vessels 

 and nerves. Accordingly, this has been esteemed a sensitive apparatus, 

 connected with the season of love in animals ; and, by other naturalists, 

 as a sense intermediate between those of taste and smell, and intended 

 to guide the animal in the proper selection of food. It need hardly 

 be said, that this is all imaginary. 



M. Adelon, 2 it was remarked, makes, two divisions of the external 

 sensations : those that convey information to the mind ; and those 

 that do not. The former have engaged attention ; the latter will not 

 occupy us long. They comprise but two itching and tickling. Both 

 of these occur in the skin and mucous membranes, and near the com- 

 munication of the latter with the skin ; or, in other words, near the 

 termination of tbe outlets which they line. Itching, however, is not 

 always an external sensation, that is, not always caused by the contact 

 of a body external to it. It frequently arises from an altered condi- 

 tion of the organic actions of the part in which it is experienced, as 

 in cutaneous affections ; in itching at the nose produced by irritation 

 in the intestinal canal ; itching of the glans penis in cases of calculi 

 of the urinary bladder, &c. ; but commonly the sensation is caused by 

 an extraneous body, and we are irresistibly led to scratch, no matter 

 how it may be caused. When it arises extraneously, it can generally 

 be readily allayed ; but, when dependent upon a morbid condition of 

 the texture of the part, it becomes a true disease, and the source of 

 much suffering. If the itching be accompanied with a feeling of motion, 

 or of purring in the part, it is called tingling. This kind of purring 

 often occurs without itching. 



Tickling or titillation is always caused by the contact of some ex- 

 traneous substance ; and is therefore a true external sensation. Although 

 occurring in the skin, and in the commencement or termination of the 

 mucous membranes, all parts are not equally susceptible of it; and 

 some, as the lining membrane of the genital organs, are only, or 

 chiefly so, under special circumstances. The sides, palms of the hands, 

 and soles of the feet, are the most sensitive in this respect ; not, per- 

 haps, because the nerves are more numerous in those parts, but because, 

 owing to thinness or suppleness of skin, or to other inappreciable cir- 

 cumstances, they are more susceptible of this kind of excitation. We 

 find, too, that individuals differ as much as the parts of the body do in 

 this respect ; some being not ticklish, or incapable of being thrown 

 into the spasm, which the act, nay, even the threatening of the act, 

 produces in others. Cases are on record, in which prolonged titilla- 

 tion has caused general convulsions, and even death. Le Cat 3 terms 



1 Annales clu Musee, xviii. 412. 



2 Physiologic de 1'Homme, 2de edit., i. 481, Paris, 1829. 

 Traite des Sens, Paris, 1767. 



