SKULL 113 



temporal fossa is usually separated from the orbit by a bar formed 

 from the post frontal or postorbital and the jugal ; it may be 

 further subdivided into a dorsal and a ventral portion by a bridge 

 of bone, the upper zygomatic arch or superior temporal arcade, formed 

 by processes of the postfrontal and squamosal (or paraquadrate). 

 The jugal may be connected with the quadrate by the quadrato- 

 jugal (or paraquadrate), thus forming a lower zygomatic arch or 

 inferior temporal arcade. 1 



In the nomenclature of the cranial bones of Reptiles much 

 confusion exists. According to Gaupp, all Crocodiles, Chelonians, 

 Lizards, and most Snakes possess a squamosal ; all Crocodiles and 

 almost all Chelonians and Lizards a paraquadrate (cf. p. 82) ; but 

 none of the above possesses a quadrato-jugal (quadrato-maxillary). 

 In Hatteria the latter is present united with the well-developed 

 paraquadrate. while the squamosal appears to be entirely wanting. 

 In narrow-mouthed Snakes all three of these elements are absent 



A number of bones arise in connection with the lower jaw 

 which includes remains of Meckel's cartilage ; viz., a dentary 

 angular, supra-angular, splenial, coronary, and articular. 



Thus it will be seen that the number of investing bones in the 

 reptilian skull is very considerable, and it may be convenient to 

 enumerate them in this place : parietal, frontal, nasal, squamosal, 

 prefrontal, septomaxillary, postorbital, jugal and quadratojugal. 

 lacrymal, paraquadrate, parasphenoid, premaxilla, maxilla, vomer, 

 palatine, pterygoid, transpalatine, dentary, angular, supra-angular, 

 splenial, and coronary. In addition to these integral and typical 

 elements, a number of less constant accessory bones occur in 

 many forms (e.g. among Lizards) e.g. supraorbitals, supraoculars, 

 supratemporals : they arise as ossifications in the derm compara- 

 tively late. 



In consequence of the absence of branchial respiration during 

 development, the hyobranchial apparatus plays a less important 

 part in Reptiles than in the Anamnia and thus undergoes reduc- 

 tion, in some cases only traces of it remaining. 



The chief points characteristic of the skull in the different 

 Orders of Reptiles are enumerated below, and for further details 

 the reader is referred to Figs. 80-86. 



Rhynchocephali. In Hatteria (Fig. 81) a fenestrated inter- 



1 The squamosal ami paraquadrate take part in various ways in the forma- 

 tion of upper and lower zygomatic arches or superior and inferior temporal 

 arcades (cf. p. 106), and according to the relations of the temporal bones three 

 types may be distinguished amongst the Amniota in general, as well as in 

 Amphibia, as follows : (1) ategokrotopkic typt (temporal region covered) Gym- 

 nophiona, Stegocephali, the most primitive Reptilia, and Marine Chelonia ; ('2) 

 zygokrotaphic type (with one or two zygomatic arches, derivable from (1) : a, 

 with lower zygoma only Anura and Aves : b, with upper zygoma only many 

 Tritonidie, most Lacertilia, Chelonia, and Mammalia : c, with upper and lower 

 zygomatic arches Tylototriton, Rhynchocephali, many fossil Reptilia, Croco- 

 dilia ; 181 gymnokntapkie ti-j^. (temporal region uncovered) most Urodela, 

 all Ophidis, some Lacertilia. Chelonia, and Mammalia. 



