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Show 1874.] MR. A. SANDERS ON THE MYOLOGY OF PHRYNOSOMA. 71 8. Notes on the Myology of the Phrynosoma coronatum. By ALFRED SANDERS, M.R.C.S., F.Z.S., Lecturer on Comparative Anatomy at the London Hospital Medical College. [Eeceived November 27, 1873.] From several specimens of lizards, for which I was indebted to the courtesy of M r . Garrod, I selected the subject of the present memoir, thinking, and as the event proved, correctly, that the singularity of its external form might be correlated with equal singularities in its muscular arrangements. According to Dumeril and Bibron * the genus Phrynosoma comprises three species. Of these, a figure of one, P. harlanii, is given in Cuvier's Animal Kingdom by Griffiths, under the name of Agama cornuta, and of another by Wiegmannf, P. orbiculare ; but neither of these figures corresponds exactly with m y specimen, differing as they do in slight details; but the description of the third species, P. coronatum, agrees better than either, and it is therefore this name which is adopted in the following pages. This animal, as well as Liolepis belli, a memoir on the myology of which I had the honour of presenting to the Zoological Society last year £, belongs to the family of the Iguanas. As will be seen, the arrangement of its muscles differs considerably from that of Iguana tuberculata, an exhaustive treatise on which was read by M r . Mivart in 1867§. Platysma myoides (fig. 1, P.M.). This muscle resembles the one which occurred in Liolepis belli. Its anterior fibres run transversely from one ramus of the mandible to the other superficially, being inserted into the inner edge for the whole length, with the exception of a small portion anteriorly ; the posterior fibres are inserted into the connective tissue at the side of the neck. At the outer edge of the muscle a few fibres are separated from the remainder by a small interspace ; but in the mid line they are all continuous ; the posterior border is situated slightly in front of the anterior edge of the muscles of the shoulder. This muscle appears to correspond to the thin plane of muscular fibre marked by M r . Mivart in the memoir above referred to as mylo-hyoid in front, and platysma myoides behind ; but in the present subject it is one continuous muscle. That it is not the mylo-hyoid is plain ; for it has no attachment to the hyoid bone ; moreover the true mylo-hyoid, which is absent in Phrynosoma, is to be found in Liolepis belli, which also possesses the homologue of this platysma. If the above interpretation be correct, on the removal of this muscle we immediately come to the Genio-hyoglossus (fig. 1, G.H.), which arises from the distal extremity of the thyro-hyal and its second segment for about half its length ; the superficial fibres pass forward and are inserted into * Erpetologie Gen^rale, torn. iv. p. 314. t Herpetologia Mexicana, tab. viii. fig. 1. + P. Z. 8, 1872, p, 154. § Ibid. 1867, p. 706, |
