AND AVES OF NORTH AMERICA. 



179 





the other Reptilian typos. An. important section of the order possesses the zygosphen 

 articulation. This is universal in the Ophidia, and exists in one family of the Lacertilia 

 the [guanidae. In the former order it is placed at a considerable elevation above the 

 zygapophyses, while in the latter family it is nearly in the plane of the zygapophyses, thus 

 occupying a lower position. The structure in the Pythonomorpha is of the latter charac- 

 ter. In species intermediate between this form and the more simple one in the orders 

 the zygosphen is found in a radimental condition. 



The diapophyses present the vortical costal articular face of Ophidians and Lacer- 

 tilians. The immensely long tail, used as a powerful swimming organ, is in truly serpen- 

 tine proportion, while its chevron bones are a lacertian rather than ophidian character. 



The prootic extends from the basioccipital to the parietal, and overlaps the latter by 

 its superior anterior margin. This does not occur among Lacertilia except in aberrant 

 forms, but is common to all serpents. There is a strong superior and anterior ala on the 

 sphenoid, which furnishes part of the suture. 



The ribs are cylindrical throughout much of their length, and resemble those of the 

 Boas in their articulation by a compressed vertical head to a vertically compressed diapo- 

 physis. There is no attached parapophysis as in the serpents. 



With respect to the characters in which this order is identical with the Lacertilia, the 

 following observations may be made. 



The brain case appears to be unossified anteriorly, as in Tortoises, Crocodiles, and La- 

 certilians; and the parietal, both descends as in Testudinata, and the ali-spenoid ascends, 

 as in Crocodilia. 



The extensive union of the o. o. palatina and maxillariais a character of Lacertians and 

 other Saurian orders, and the existence of separated hypapophyses is a feature seen in a 

 few existing Lacertilians. These separate elements are articulated to heavy cylindric 

 fixed hypapophyses, which are characteristic of the cervical vertebrae of this whole group 

 with the exception of one genus. Though the separation of the extremital pieces is La- 

 certilian, they are in the latter sessile, and the great length of the whole hypapophysis 

 paralleled by those of the serpents. 



The scapula and coracoid are not very different from those of Lacertians, and are not 

 coalescent. The scapula appears to have had an angle or process similar to the procora- 

 coid, while the coracoid is entirely without the emarginations common to Lacertilia. No 

 trace of claviculus, mesosternum or xiphisternum has been found. On the whole, the sca- 

 pular arch is quite as similar to that of the Sauropterygia as that of the Lacertilia. 



The os quadratum is Like that of the Lacertilia in its form, and in its support by two 

 suspensoria. It; is as mobile, but much shorter than, in the serpents, and differs from that 

 of both these orders in nearly enclosing the meatus auditorius behind by a Large decurved 



