22 POSTBEIOR CRANIAL ARCHES 



IV. A supratemporal foramen only. 



Zygomatic and supratemporal arches present and not separated bj- an infratemporal foramen, 



Pseudoauchia. 

 A supratemporal and no zygomatic arches ; a paroccipital Lacertilia. 



Pythonomorplia. 



V. No arches or foramina. 



Quadrate suspended to paroccipital OpMdia. 



These structures must be considered in determining the systematic position of 

 the groups above enumerated, but their characters are not all of equal systematic 

 value. 



III. The Parietoquadeate Arch. 



This arch is not present in the Batrachia, and is very variously developed in the 

 Reptilia. It is produced by the separation of the posterior elements of the tem- 

 poral roof of the Stegocephali and Cotylosauria, from the elements of the brain case 

 below them. That is, by the development of a foramen between the supramastoid 

 and supratemporal above, and the exoccipital and paroccipital below. 



The parietoquadrate arch is a later appearance in geologic time. It is not 

 present in any of the Permian orders. The earliest indication of it is seen in the 

 Ichthyopterygia, where a space appears between the very large supramastoid above, 

 and the exoccipital and paroccipital below. It is wanting in the three Archosaurian 

 orders, but is represented by a fissure in the Triassic Belodon, and in Crocodilia in 

 general.* In Testudinata it is potentially present in the posterior part of the tem- 

 poral roof, but is only distinguished in certain Pleurodira (Hydraspis), where the . 

 supramastoid element is lost, or fused with the parietal processes which form its 

 proximal part. In the Rhynchocephalia it is well developed in Sphenodon, but here 

 also the supramastoid element is not distinct, being fused with either the supratem- 

 poral or parietal. The arch has the same character in Lacertilia, except that the 

 paroccipital sends upwards a brace along its inferior border. That this element is 

 the paroccipital has been already shown by reference to the structure in the Ichthyo- 

 saurus and in the Pythonomorpha (Fig. 3). 



The space enclosed below the parietoquadrate arch I propose to call the parieto- 

 quadrate foramen. Its presence is an indication of systematic value, but not in gen- 

 eral of a high grade. Thus among the Squamata it is absolutely wanting in Ophidia, 

 and is scarcely elevated above the exoccipital in some Pythonomorpha. In Lacer- 

 tilia the foramen is much reduced in Feylinia, and is wanting in Anniella and the 

 AraphisbsBnia, while it is large in most other types. 



*See Deslongchamps, E., Notes Paleontologiques, I, 1868-9, Caen et Paris. 



