256 MR, F. E. BEBDAKD OX THE ANATOMY [Juiie 6, 



5. Some Notes upon tbe Anatomy of the Yellow-throated 

 Lizard, Gerrhosmirus fiavigulans. By F. E, Beddard, 

 F.R.S., Prosector to the Society. 



[Received Maj- 17, 1905.] 



(Text-figures 33-38.) 



Apart from osteology * and a few scattei'ed notes, which will 

 be referred to in the course of the present communication, there 

 does not appear to be a great deal known about the internal 

 structure of Gerrliosaurus. Inasmuch as this Lizard is regarded, 

 from the point of view of external characters and osteology, as 

 being exactly intermediate between the Lacertida? and Scincidse t, 

 it seemed to me interesting to attempt a criticism or confirmation 

 of this view, while recording anj^ new facts which an investigation 

 of Gerrhosaurus flavigularis might bring to light. 



Jugal Ligament. 



Many, but not all, of the Lacertiiia possess, as is well known, 

 a jugal ligament, which Huxley compared to the bony lower 

 temporal arcade of Hatteria. The exact relationships of this 

 ligament have not, I believe, been described in some of the 

 Lizards in which I shall now proceed to detail the arrangement. 



It is possible to recognise several stages in the conditions of the 

 jugal ligament, which may i-epresent evolutionary stages, though 

 it is, of course, not implied that the genera to be mentioned are 

 genetically connected in the order named. 



In Iguana tubercidata the ligament as a distinct structure is 

 totally absent. On cutting through the skin covering the " cheek,'" 

 the muscles and bones of this region of the skull are at once 

 arrived at. It appeared to me, however, that the subcutaneous 

 connective tissue, which is dense and white in most parts of the 

 body, was rather denser and whitei- in the region wliere the jugal 

 ligament would be were it present. It is possible, in fact, that in 

 this lizard an early stage is met with — that the ligament is not 

 yet differentiated from the general connective tissue of the skin. 

 On the other hand, it cannot be denied that the same fact may be 

 explained on the theory that the ligament has disappeared. In 

 any case, Gerrhosaurus offers an intermediate condition. In this 

 reptile the ligament in question is anchored firmly to the quadi-ate 

 behind, but in front it is not attached to the jugal bone but to 

 one of the bony scales which cover the face in this region. That 

 is to say, the ligament has not as yet completely detached itself 

 from the skin. So, at any rate, the facts seem to indicate. It is 

 important to notice in connection with the main object of the 

 present communication, viz., to attempt to fix the systematic 



* Siebenrock, Ann. k. nat. Hofmus. Wien, vii. 1892. 

 t Boulenger, Cat. of Lizards. 



