144 ANNALS NEW YORK ACADEMY OF SCIENCES 



Adductor operculi and levator operculi. — These are closely associated. 

 Both arise on the posterior part of the skull in the otic region and are 

 inserted on the inner side of the opercular bone. Often one of them is 

 absent or perhaps they are not differentiated. They are present in almost 

 all the Pisces with the exception of elasmobranchs. They are small in 

 the dipnoans. 



Homology of the Jaw Muscles in the Amphibia 

 (Table II) 



There is quite a difference between the muscles of the Pisces and those 

 of the Amphibia, for in the latter muscles masses have become more spe- 

 cialized by a splitting off of the different slips, so that they may be called 

 separate muscles. Some of these divisions were suggested in the Pisces 

 by the direction of the fibers and by differences in the origin and inser- 

 tion, but they remained a part of the parent mass, as they do, for the 

 most part, also in the Eeptilia. In the Amphibia the muscles of the 

 anterior part of the piscine head have disappeared, being represented by 

 vestiges only. Lubosch (1913, p. 71) says: 



Bisher unbekannte Muskelrudimente wurden gefunden bei Amphiuma und 

 Cryptobranchus. 



(1) Ein M. levator arcus palatini bei Amphiuma und Cryptobranchus, von 

 der knorpligen Nasseskapsel und (Amphiuma) der vertikalen Lamelle des 

 Frontale ( Wiedersheim ) entsprigend und zur Membrana pterygomaxillaris 

 zeihend. 



(2) Ein M. adductor maxillae bei Cryptobranchus vom vorderen Rand des 

 knochernen Pterygoids und dem knorpligen Proc. pterygoideus quadrati ent- 

 springend und in der Nabe des Maxillare in der Membrana pterygo-maxillaris 

 endend. Beide Muskeln werden mit feinen Aestchen aus demselben Nerven 

 verseben, wbelcher aucb die Mm. pterygoidei versorgt. 



The great changes in the skull of the Amphibia account for the reduc- 

 tion and dropping out of several of these typical piscine muscles. There 

 is no need for the levator maxillae superioris and the levator arcus pala- 

 tini, as the parts controlled by these muscles are fixed. The new form of 

 the bones demand a different musculature and the loss of others. The 

 preopercular, symplectic, hyomandibular, opercular, inter- and sub-oper- 

 cular and several of the bones of the skull and maxillary region have 

 either been lost or changed their functions, so that new muscles are 

 needed. If the hyomandibular is considered to be the stapes of the higher 

 forms, it seems to have discarded its original musculature in the transfor- 

 mation, for there are no muscles in the forms with a stapes that could 

 have been retained from the muscles of the hyomandibular. The two 

 hyomandibular muscles — the protractor (V 3 ) and the levator (VII) — 



