CROCODILIANS, LIZARDS, AND SNAKES. 689 



Liehanura, Charina, and Uryx, and to tbese must be added Xenopeltis. 

 The frontals are always distinct and the parietals are always united. 

 The supraoccipital never enters the foramen magnum, which is 

 bounded above by the exoccipitals. The prefrontals are articulated 

 above with the frontals and, in the divisions above named, Yvith the 

 nasals also. The postfrontals are present, but are small and easily lost 

 in preparing crania in some types. They are generally well developed, 

 but are small in TAehamira and Cylindrophis, and are wanting in Xeno- 

 peltis, Charina, Ilysia, the Scolecophidia, and the Elapidw. They are 

 elongate and extended forward over the orbit to the prefrontals in 

 AchrochordidsB and Nothopidae. There is a supraorbital bone in the 

 rythonidrt\ The paroccipital is included in the cranial walls in all 

 angiostomatous snakes, and is excluded from the brain case, lying 

 scale-like on the surface, in the eurystomatous families. It is short in 

 burrowing snakes, but elongates in other families, reaching an extreme 

 length in the solenoglyphous division. The maxillary bone is loosely 

 attached in Serpentes, having a close articulation with the prefrontal 

 only, except in the Epauodonta, where it is fixed firmly to the premax- 

 illary and vomers, as in lizards. It is shortened anteriorly in the Pro- 

 teroglypha, and both anteriorly and posteriorly in the Solenog]yi>ha, so 

 as to become snbvertical. Among the latter it is solid in all except the 

 Crotalidie, where it is deeply excavated by a fossa postero-exteriorly. 

 In the 0])oterodonta the maxillary is also very short and triangular, 

 articulating very loosely with the prefrontal with its narrow apex. In 

 snakes there are no lachrymal nor jugal bones. In proportion as the 

 maxillary is abbreviated posteriorly, is the ectopterygoid elongated. 

 The latter is generally a simple element, but in certain Najid genera it 

 is deeply bifurcate anteriorly, according to Boulenger. 



The lateral walls of the brain case consist apparently of the frontal, 

 parietal, and jietrosal bones, which articulate below with the presphe- 

 noid, sphenoid, and basioccii^ital elements. At the base of the orbital 

 wall of the frontal is a longitudinal groove, bounded below by the pre- 

 sphenoid, which is occupied by the more or less persistent trabecula 

 cranii. The optic foramen is large, and becomes a vacuity in types 

 with large eyes, as Bascaniiim, and according to Boulenger those of 

 opposite sides are confluent in PsammopMs. The trigeminus foramen 

 is represented l)y two, which communicate beneath a long bridge in all 

 snakes, including Typhlops {Olauconia not examined). The (luadrate 

 bone presents some diversities of form, but none of great importance. 

 In Ti/phlopfi it is short and flat, and presents a free angular process 

 anteriorly. In Glaiiconia. it is long and slender, and has no anterior 

 process. In the Tortricina it is very short, and has in the Ilysiidie a 

 cylindric shaft. In Asinea it is generally flat and expanded at the 

 proximal end, and has no angular process of the shaft, but in Eryx it 

 is not expanded, and has a triangular section. In Xcnopcltis it is short, 

 and has a short posterior projection proximally, as in lizards. In the 

 NAT MUS 98 44 



