IX. Deficiency of the Underjaw (Monona).
Want of the under jaw often coexists with Cyclopia. By this complication is formed a peculiar series of monsters, which make a gradual transition to those in which, notwith standing the presence of two eyes, the under jaw is absent. I refer to this the following species.
1. Total defect of the opening of the mouth,— as observed by me in a lamb, in which also the ears were removed to the basis of the head and coalesced. The under jaw was totally absent ; and behind the coalescent ears there was an osseous vesicular cavity, formed by the bulbous tympanic cavities, united to gether.
2. The opening of the mouth represented by a fissure at the inferior surface of the face. The rest of the external appearance is similar to the first species. The under jaw is want ing, but there is a rudiment of a tongue.
3. Too short an under jaw. In man and the lower animals the under jaw is sometimes incompletely developed, and more depressed posteriorly than it ought to be. This original brevity of the under-jaw is the cause of a great many ulterior deformities.
Without doubt, these three forms of mon strosity make a continuous series. They consist, as Bischoff says, in an imperfect developement of the first visceral arc, by which the under jaw and the bones connected there with are either wanting or defectively formed, the result of which is, that the ears are re moved to the basis of the head, and there become fused together. The total defect of the opening of the mouth is the highest, the too short under jaw the least degree of mal formation.
Herewith I conclude my brief account of the monstrosities resulting from arrest of de velopernent. The description of the congenital abnormal condition of the different apparatus would oblige me to surpass the due limits of an Article for this Cyclopmdia, which already, I fear, may be considered rather too long ; and I think this the less necessary, because a great deal of information about them may be found in the Articles ANUS, DIAPHRAGM, FmTUS, HERMAPHRODITISM. I therefore pass on to a succinct description of a second group of monstrosities.