Mat 21, 1915] 



SCIENCE 



763 



recommended to the general reader also, be- 

 cause the style is simple and the ideas are 

 clearly and logically developed and followed. 

 With the growing interest in metallography 

 as a method of testing and of research it will 

 undoubtedly prove very popular. 



W. Campbell 



SPECIAL ASTICLES 



THE TEMPORAL FOSSAE OF VERTEBRATES IN RELA- 

 ■ TION TO THE JAW MUSCLES 



About two years ago one of us (Gregory) 

 discovered that the superior and lateral tem- 

 poral fenestrsB of all two-arched reptiles and 

 the single fenestra of all one-arched reptiles 

 appear to be related to the jaw muscles in such 

 a way that they either give exit to them upon 

 the top of the skull or afford room for them 

 at the sides. It was afterward learned that 

 Dollo'^ had reached the same conclusion in 

 1884, but his important results have been prac- 

 tically ignored in the subsequent literature of 

 the temporal fenestrse, which have been con- 

 sidered too largely from a purely taxonomic 

 viewpoint and too little with reference to their 

 adaptational sig-nificance.^ 



More in detail, the steps leading to the pres- 

 ent note were chiefly as follows : 



It was observed that the temporal fossse of 

 Cynognathus and other Theriodonts present 

 close resemblances to those of primitive mam- 

 mals and it thus seemed highly probable that 

 in these reptiles the sagittal and occipital 

 crests, together with the zygomatic and post- 

 orbital borders, bounded the homologue of the 

 mammalian temporalis muscle. Comparison 

 with the snapping turtle Ohelydra suggested 

 that in this case also the backwardly prolonged 

 sagittal crest served for the attachment of the 

 temporalis; and this gave added significance 

 to the immense temporal fossae and massive 



1 ' ' Les Muscles fleveurs de la Mandibule et leur 

 Influence sxix la Forme du Crane: Cinquifeme Note 

 Eur les Dinosauriens de Bemisaart," Bull. Mus. 

 Soy. Hist. Nat. Belg., Tome III., 1884, pp. 136- 

 146. 



2 A partial exception to this statement is af- 

 forded by Professor Lull's well-studied reconstruc- 

 tion of the cranial musculature of Triceratops 

 (Amer. Jour. Sei., Vol. XXV., 1908, pp. 387-99). 



mandible of Ohelone. The partial excavation 

 of the dorsal roof over the temporal muscles 

 in Ohelydra appeared to give this muscle more 

 room for action, and the almost complete re- 

 moval of the temporal roof in Trionyx seemed 

 to give further evidence in the same direction. 

 In Sphenodon it was seen that the borders 

 of the superior temporal fenestrse apparently 

 served for muscle attachment, and dissection 

 of a specimen of this animal showed that this 

 inference was correct, and that the lateral 

 temporal fenestrse gave room for the expansion 

 and contraction of the voluminous muscle 

 mass. It was further recalled that in the most 

 primitive Tetrapoda (stegocephalians and 

 eotylosaurs) as well as in primitive Osteich- 

 thyes (Polypterus, Devonian Rhipidistia, 

 Dipnoi, etc.) the temporal region is completely 

 roofed over, while modernized forms such as 

 Urodeles, Anura, lizards and snakes have the 

 outer temporal roof reduced to slender bars or 

 even entirely absent. The presence of a sag- 

 ittal crest in Amphiuma indicated that in the 

 modernized Urodeles the temporal muscles had 

 extended on to the top of the skull. From 

 such observations the following inferences were 

 drawn: 



1. That in primitive vertebrates the chief 

 temporal muscle-mass (adductor mandibulae 

 of sharks) was originally covered by the dermal 

 temporal skull-roof. 



2. That in modernized Amphibia and Eep- 

 tilia, as well as in birds and mammals, one or 

 more slips of the primitive adductor mass had 

 secured additional room for expansion by per- 

 forating the temporal roof either at the top or 

 at the sides or in both regions at once; much 

 as in hystricomorph rodents a slip of the 

 masseter has invaded the region of the infra- 

 orbital foramen, so that it now extends through 

 a widely open arcade and finds room for ex- 

 pansion on the side of the face. 



3. A comparative study of the skull of 

 Tyrannosaurus,^ in connection with the above- 

 mentioned observations and conclusions, led 

 to the 'suspicion that the antorbital fenestras of 



3 Partly embodied in Professor Osborn 's memoir 

 on Tyrannosaurus, Mem. Amer. Mus. Nat. Hist., 

 N. S., 1912, Vol. I., Pt. I. 



