The Facial Musculature of some Lesser Primates and a Tupaia. A Comparative Study.

Authors


  • Communicated by Prof. J. P. Hill, D.Sc, F.R.S., F.Z.S.

Abstract

Summary.

The facial musculature of four types of Mammals—one Subprimate and three Primates—has been examined. It has been described under five headings, viz.:—platysmal, superior pre-auricular, oral, retro-auricular, and stylo-hyoidean. This classification indicates the matrices from which each group is derived as closely as is consistent with descriptive anatomy. The platysma was well developed in all except the lemurs, in which it failed to attain attachment to the nuchal, omoidean, clavicular, or genal regions; it has, therefore, been called degenerate. Trachelo-platysmæ were present only in the lemurs and marmoset; no platysmal derivates were found. Of the superior preauricular group, the M. orbicularis oculi was remarkable in the Tupaia and Tarsius; in the former on account of the break in the inferior distal fibres and the attachment to the zygoma of the central fibres. In Tarsius the muscle was of unusual size and had unusual anterior attachments. At present it is difficult to say if these latter represent a primitive condition laid bare, so to speak, by the apparent overstretching of this muscle to such an extent that it is only one fibre in thickness; or whether it is a specialization peculiar to Tarsius. In each of the specimens the M. orbicularis oculi was, laterally, directly continuous with a large superficial orbito-auriculo-labial sheet; in Tupaia this was incomplete. In each specimen the lower margin of this sheet was formed by the M. auriculo-labialis inferior. In the lemurs the muscle lies upon the same plane as, and is closely apposed to, the upper margin of the portio modiolaris platysmæ, as the platysma in this Primate is devoid of a pars supra-angularis. This led Ruge to consider the M. auriculo-labialis inferior as a portion of the platysma. In Tarsius, however, the former runs deeply and obliquely to, and is unconnected with, the partes supra-angularis and modiolaris platysmse, and in consequence the muscle has been classified with the superior pre-auricular musculature. A M. naso-labialis was present in each specimen, but it differed from that of the dog, as figured by Huber, in that its fibres extend over the medial frontal region. No M. angulo-naso-labialis (caput angulare) was present in any specimen, though in Tarsius a M. infra-orbito-labialis (caput infra-orbitale) was well developed. Of the oral group the M. orbicularis oris of each Primate showed a division into partes marginalis and peripheralis, and in Tarsius the arrangement of these fibres resembled that seen in Anthropoids and Man. In each specimen a M. maxillo-naso-labialis was present. With the retro-auricular group has been classed the M. digastricus posterior and the M. cervicalis transversus. This latter has formerly been considered as a deep layer of the platysma, but the innervation would seem to preclude this.

Bibliography.

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