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Show 456 MR. ST. GEORGE MIVART ON THE [Jlllie 24, The other part of the digastric (figs. 1, 2, & 3, D. 1) is larger, springs from the dorsal end of tbe first branchial arch (above the attachment of the levator arcus primi), and is inserted behind the first part into the tendon before mentioned. Levatores arcuum* (figs. 1, 2, & 3, L. A, & L.A.I, also fig. 2, L.A.P). These are much developed, and the one going to the first branchial arch is remarkably distinct from the rest. This, the levator arcus primi (fig. 2, L.A.P), is quite hidden until the digastric is pulled outwards and the anterior part of the dorsolateral muscular mass inwards towards the middle line. When this is done the levator arcus primi is to be seen passing outwards and backwards from the exoccipital and opisthotic to the anterior margin of the first branchial arch, very near its superior extremity. The levatores* oi the second and third branchial arches arise mainly from the dorsal fascia ; but the most anterior part (figs. 1 & 2, L. A. 1) seems to be differentiated off from the anterior end of the dorso-lateral muscular mass, and covers, and is similar in direction to, the hidden levator arcus primi. In the figure, between the most anterior part (fig. 1, L. A. 1) and the first part of the digastric (fig. 1, D. 1) a portion of the anterior end of the dorso-lateral muscular mass is seen to be interposed. Mylo-hyoideus anteriorf (figs. 4 & 5, M. II. 1). This muscle is relatively smaller than is its homologue in Menopoma. It arises from tbe inside and lower border of the ramus of the mandible, and unites with its fellow of the opposite side without forming any distinct longitudinal tendinous interval. The mylo-hyoideus posterior X (figs. 3, 4, & 5, M. II. 2) is a considerable muscle, the postero-inferior part of which is enclosed on both sides by the skin forming a free fold or opercular flap beneath the throat. The muscle arises from the dorsal segments of the hyoidean cornu and first branchial arch, also from the fascia investing externally the voluminous cerato-hyoideus externus. Passing downwards it unites with its fellow of the opposite side, a sort of linea alba marking their junction. At its anterior part this muscle is placed above the mylo-hyoideus anterior, the latter being superficial to it. I could find no trace of the muscle which I have described in Menopoma as the constrictor faucium. Constrictor pharyngis§. This consists of two parts: one (the dorso-trachealis) arises from the fascia external to the dorso-lateral muscular mass behind and beneath the levatores arcuum; the other (the hyo-trachealis) springs from the postero-ventral surface of the third branchial arch. The fibres converge and join the fellow muscle of the opposite side beneath the trachea. The genio-hyoideus \\ (fig. 4, G. II) is a rather long narrow muscle * Fischer, /. c. p. 81, tab. iii. B. la. t Fischer, I. c. p. 41. } Fischer, /. c. p. 42. § Fischer, I. c. p. 89. | Fischer, /. c. p. 5'}. |