400 me. e. w. HooLEr on the [June 19 13,. 



the jngal and quadratojugal thereby are surprising characteristics- 

 and isolate 0. latidens from every known family. Hermann von 

 Meyer 1 describes the jugal of Pterodactylus longirostris (syn. Pt. 

 antiqitus) as forming the under and greater part of the anterior 

 boundary of the orbit by a strong, pointed, outgrowing process. 

 In Pt. scolopaciceps (syn. Pi. leochi) 2 he gives an almost similar 

 plan; and the jugal in Pt. crassirostris 3 (syn. Scaphognathus 

 crassirostris) he describes as a four-branched bone forming the- 

 under half of the orbits. Thus there is no arrangement approaching 

 to that which obtains in Ornitlwdesmns latidens ; but Scaphognathus 

 purdoni reveals at least an incipient stage. Mr. Newton 4 says that 

 the jugal in this species is ' a V-shaped bone,' and that the hinder 

 branch 'has its posterior edge occupied by the quadratojugal.' 

 Dr. G. Baur, 5 in some pertinent notes on Mr. Newton's paper, 

 remarks that 



' the tendency of the quadratojugal in Scaphognathus to separate the post- 

 orbital from the jugal is very remarkable.' 



This process of the exclusion of the jugal from the supra-temporal 

 arcade is apparently an adaptive result. In Orniihodesmus the 

 prolongation of the facial portion of the skull is about 5| times 

 that of the cranial, and in Pterodactylus antiquus, the nearest to 

 it in shape, 3^ times ; while in Scaphognathus crassirostris it is- 

 1| times. This proportion in the two last-named permits of the 

 vertical position of the jugal process, to meet the lachrymal; but 

 in Omitliodesmus latidens the proportion of the length of the beak 

 to that of the cranium is so much greater, that not only the jugal,. 

 but also the quadratojugal and quadrate have become elongated 

 forwards, until the entire jugal, the greater part of the quadrato- 

 jugal, and the quadrate are in front of the orbit. The posterior 

 production of the maxilla to the quadrate has not originated this 

 disposition of the jugal, for the position of the hinder extremity 

 of the maxilla in Pterodactylus and in Scaphognathus is the same 

 as in Orniihodesmus, namely, beneath the posterior third of the 

 antorbital vacuity ; and this is its location in Pterodactylus antiqitus,. 

 Pt. hochi, Pt. suevicus, Dimorphodon, FJianiphorhynclms, and 

 Omithostoma : it cannot be directly for the reduction of the weight 

 of the skull, for in Dimorphodon the maximum had almost been 

 attained. It must he that the prolongation of the beak, which 

 was more favourable to the reptile in procuring food, has drawn 

 out and displaced the jugals, the quadratojugals, and the quadrates,. 

 to the extreme. The great length of the lower temporal arcades 

 in antero-posterior extent is in striking contrast with their short- 

 ness in Pterodactylus, Scaphognathus, Dimorphodon, Ptenodracon,. 

 Omithostoma, and Nyctosanrtis. 



1 ' Eeptilien aus dem Lithogr. Scbiefer d. Jura' 1860, p. 27. 



2 Ibid. p. 33. 3 Ibid. p. 41. 



4 E. T. Newton, Phil. Trans. Eoy. Soc. ser. B, vol. clxxix (1888) p. 505. 



3 Geol. Mag. dec. 3, vol. vi (188 C J) p. 173. 



