Tongue movement in the cat during the intake of solid food.

During feeding, solid food in the mouth progresses towards the pharynx during transport cycles, but it does not do so in chewing cycles. In the cat, the two cycle types differ with respect to jaw and hyoid movement but it is not known if, or how, any differences in tongue movement arise. This study sought to quantify the tongue movements in the different cycle types. Radio-opaque markers were placed in the midline of the cat tongue. While the animals ate solid food, the marker movements (viewed in the sagittal plane) were recorded by cine-radiography. The movement of the tongue relative to the palate could be split into three components derived from (a) movement of the mandible, (b) movement of the hyoid, (c) movement produced within the body of the tongue itself. Although the differences in jaw movement between transport cycles and chewing cycles produced some differences in tongue movement relative to the palate, differences in the movements produced within the tongue itself were of greater significance. Transport cycles were characterized by rhythmic extensions of the tongue; the protracted tongue was about 60% longer than the retracted tongue. In chewing cycles, rhythmic length changes (viewed in the sagittal plane) were reduced and could be partly explained by an associated rotation of the tongue. In transport cycles the tongue, with food on it, was elevated to the palatal rugae as it extended, but when it shortened it was out of contact with the palate. It is suggested that these movements form the basis of a transport mechanism.