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. 



[Received November 27, 1873.] 



From several specimens of lizards, for which I was indebted to 

 the courtesy of Mr. Garrod, I selected the subject of the present 

 memoir, thinking, and as the event proved, correctly, that the sin- 

 gularity of its external form might be correlated with equal singu- 

 larities 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 comuta, and of another by 

 Wiegmannf, P. orbiculare ; but neither of these figures corresponds 

 exactly with my 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 Mr. 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 Mr. 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 iu Phrynosoma, is to 

 be found in Liolepis belli, which also possesses the homologue of 

 this platysma. If the above interpretation be correct, on the re- 

 moval of this muscle we immediately come to the 



Genio-hyoglossus (fig. 1, G.H.), which arises from the distal ex- 

 tremity of the thyro-hyal and its second segment for about half 

 its length ; the superficial fibres pass forward and are inserted into 



* Erpetologie Generale, torn. iv. p. 314. 



f Herpetologia Mexicans, tab. viii. fig. 1. 



+ P. Z. S. 1872, p. 154. § (bid. 1867, p. 766, 



