The masticatory muscles are the ones of particular academic interest: they are the principal effectors for the various jaw movements during the act of mastication; also they cause intricate changes in facial blood distribution and in dental occlusion during the act of mastication and various facial expressions. Of the masticatory muscles the temporal muscle is especially rich in morphological variations in terms of race, individual, laterality, sex and age. Many papers have been published on the muscle not only in the discipline of anatomy but in those of oral surgery, otorhinolaryngology and dentistry. Most of them put emphasis on its functional aspect rather than its morphological aspect. Few have reported on the morphology of the temporal muscle, and fewer on the subject in relation to the process of its development and growth.
In this paper the author investigates the growth of the temporal muscle morthometrically in relation to the one of the skull : the former is represented by the elevation of the inferior temporal line which delineates the limit of origin of the muscle ; the latter by both Martin-Saller's and the author's parameters of measurements of the skull. The materials examined were 21 juvenile and 52 adult Indian skulls, which are divided by Hamada's method of classifying according to dental eruption into four classes : 12 skulls in the late deciduous dentition stage (three to five years of age), five in the early mixed dentition (six to seven years of age), four in the middle mixed dentition (eight to nine years of age) and 52 in the permanent dentition (15 to 35 years of age).
The following results were obtained:
1) The Indian skulls show gradual growth from the late deciduous to the early mixed dentition stage, more gradual growth from the early to the middle mixed dentition stage and rapid growth from the middle mixed to the permanent dentition stage.
2) The temporal muscle in terms of the inferior temporal line also follows the same growth pattern.
3) The inferior temporal line is relatively higher in adult than in juvenile skulls. This indicates that the temporal muscle enlarges up the side of the skull in response to the increased demands of mastication consequent upon the eruption of teeth. The origin of the muscle wanders forwards and upwards in the late deciduous to the early mixed dentition stage, but largely back wards and upwards in the middle mixed to the permanent dentition stage.