764 



SCIENCE 



[N. S. Vol. XLI. No. 1064 



dinosfiurs, phytosaurs, pterosaurs, etc., were 

 also functionally connected with the muscles 

 of mastication; but it was realized that proof 

 of this view required a wider study of the jaw 

 muscles of living reptiles. It was afterward 

 found that Dollo (1884) had suggested that the 

 antorbital fenestree of extinct reptiles were 

 filled by the pterygoid muscles. 



4. With regard to the supposed relations of 

 the mammals with the Theriodont reptiles, it 

 was thought that some light on the origin of 

 the mammalian alisphenoid and pterygoid and 

 on the probable steps in the transformation of 

 the reptilian into the mammalian condition 

 could be obtained by a study of the muscles of 

 the pterygoid region in existing reptiles and 

 mammals. 



5. The supposed transformation of the rep- 

 tilian quadrate, articular and angular, into the 

 mammalian incus, malleus and tympanic, 

 respectively, as held especially by Gaupp,* 

 Gregory, '^ Broom" and Watson,' might, it was 

 thought, be further elucidated by a careful 

 reconstruction of the jaw muscles of Cynog- 

 nathus and by a study of the muscles of the 

 middle ear in mammals (m. stapedius, m. 

 tensor tympani). 



6. In directing the studies of graduate stu- 

 dents upon the structural and phylogenetic 

 history of the skull in vertebrates it was found 

 advantageous to emphasize the functional 

 meaning and importance of the chief openings 

 in the skull, and to consider the osseous ele- 

 ments in the temporal and pterygoid regions 

 as if they were mere remnants, or tracts of 

 bone, resulting from the reduction of an 

 originally continuous dermal covering, through 

 the moulding influences of the jaw muscles. 



7. In comparing the skull patterns of the 

 oldest Osteichthyan fishes (Dipnoi, Ehipidi- 

 stia, etc.) sutures came to be regarded as loci 

 of movement or progressive overgrowth, con- 

 ditioned in part by muscular action, while 



«"Die Reiehertsche Theorie," Archiv. fiir Anat. 

 und Entw., Supplement Band, 1913. 



^Bull. Amer. Mus. Nat. Sis., Vol. XXVII., 

 1910, pp. 125-143; Jour. MorpJi., Vol. XXIV., 

 1913, pp. 23-35. 



eProc. Zool. Soc, 1912, pp. 419-25. 



7 Proo. Zool. Soc, 1914, pp. 779-85. 



centers of ossification were considered as loci 

 of relative stability. 



At this point the junior author of the pres- 

 ent note undertook to make a broad and at the 

 same time sufficiently detailed study of the 

 jaw muscles of vertebrates, partly with the 

 view of testing and extending the foregoing 

 observations and conclusions. 



It was soon found that while many anato- 

 mists had made intensive studies of the inner- 

 vation of the muscles of mastication in certain 

 types very few had attempted to follow them 

 throughout the vertebrates and no one had 

 given an adequate series of figures. It is in- 

 deed a surprising fact that comparative myol- 

 ogy is so briefly treated in the standard text- 

 books. The work has been carried on in the 

 laboratory of vertebrate evolution in the 

 American Museum of Natural History. A 

 series of 26 existing types of vertebrates has 

 been studied and figured as follows: Elasmo- 

 branchii 1, Chondrostei 2, Holostei 1, Teleostei 

 3, Crossopterygii 1, Dipnoi 1, Urodela 3, Anura 



1, Chelonia 1, Ehynchocephalia 1, Lacertilia 



2, Crocodilia 1, Aves 1, Mammalia 7. In 

 each case special attention has been paid to the 

 innervation of the muscles as a guide to 

 homologies. By means of these data, and of 

 the principles that became apparent as the 

 work proceeded, reconstructions of the jaw 

 musculature were attempted in the following 

 series of extinct forms : DinicMhys (Arthro- 

 dira), Eryops (Temnospondyli), Labidosaurus 

 (Cotylosauria), Cynognathus (OynodontiEe), 

 Tyrarmosaurus (Theropoda). The full results 

 of this study will be published elsewhere by 

 Adams, but meanwhile it may be worth while 

 to record the chief general conclusions which 

 we have reached in collaboration. 



1. It seems impossible to work out the jaw 

 musculature of DinicMhys either on the 

 dipnoan or on the ordinary teleostome bases 

 and a study of the muscle areas by Adams 

 indicates a unique type of jaw movements, a 

 fact of no little phylogenetic significance, in 

 view of the disputed relationships of this 

 group. 



2. The above mentioned conclusions of 

 Dollo and of Gregory regarding the origin of 



