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Show 160 DR. R. W. SHUFELDT ON l^Pr- U take on the same direction as the fibres of the temporalis, of which it seems almost to be the anterior part, and passing downwards aud forwards, they are inserted, being somewhat tendinous, into the inner aspect of the ramus of the mandible, below and at the same time behind the coronary process1. 6. Neuro-mandibularis.-Both this and the next muscle are but feebly developed in our present subject, and so much alike are they, both in their origins and insertions, as well as in the direction of their fibres, that one might easily mistake them for one and the same structure. The neuro-mandibularis is the more posterior of the two, and upon either side it arises from the hinder free margin of the parietal bone, from its mid-posterior point for a distance outwards of about four millimetres. It is thin and tendinous here, but soon gathers itself into a small, somewhat laterally flattened, bundle of fibres which pass directly downwards to the posterior tip of the mandible, where they make a firm tendinous insertion. 7. Digastric.-Is rather a smaller muscle than the neuro-mandibularis, being related to it as we have already described in the foregoing paragraph. It is the muscle of the deep layer which goes to form the posterior fleshy border of the aural opening, the mylo-hyoideus posterior being the superficial one. It arises from the point of meeting of the quadrate, squamosal, and parietal bones, at the postero-lateral aspect of the cranium, and passes directly downwards to make a common insertion with the neuro-mandibularis on the hinder end of the lower jaw. Mivart does not allude to the neuro-mandibularis as occurring iu either Parson's Chamseleon or in the Iguana, while Sanders describes it as being present in Phrynosoma, as well as in Liolepis. Hoffmann recognizes it in his general account of the myology of Lizards, while again Mivart (Elem. Anat. p. 311) figures two digastrics for Menopoma, the posterior one of which I take to be the neuro-mandibularis. Muscles of the Hyoidean Apparatus, 8. Genio-hyoideus.-This is a fiat muscular sheet composed of fasciculi of coarse fibres, which, with the fellow of the opposite side, forms a substantial fleshy underflooring to the buccal cavity. Either genio-hyoid arises, carneous, from the entire anterior surface of the corresponding thyro-hyal of the hyoid, and its fibres, converging but very slightly, pass directly forwards to become inserted along the inner aspect of the ramus of the mandible for the middle third of its length. The deeper fibres of this muscle pass upwards to become inserted into the base of the tongue. This muscle is inclined to be more tendinous at its insertion than it is at its origin, where in front it is separated from its fellow by quite an interval. 9. Cerato-hyoideus.-By dividing the genio-hyoideus transversely through its middle and reflecting back the cut extremities, we expose the deeper set of the hyoidean muscles. The cerato-hyoideus 1 I fail to find a " superficial temporal" in this lizard, as is described by Mivart in Chamceleon parsouii (P. Z. S. 1870). |