610 
F. H. EDGEWORTH. 
genio-liyoid, stylo-glossus, and liyoglossus), whereby a series 
ol long retractors of the front end of Meckel’s cartilage and 
of the tongue are formed. Though such retractors may pos- 
sibly play a part in the formation of the new jaw-joint in the 
individual, yet the absence of any uniformity in their develop- 
ment suggests that they did not do so in its phylogenetic 
development. 
-It has generally been supposed that the formation of the 
new squamoso-mandibular joint was associated with the dis- 
appearance of a depressor mandibulge. As is stated later 
fp. 630), there is no ontogenetic evidence of the disappear- 
ance of such a muscle, and comparison of the early stages of 
the hyoid muscles of Amphibia and Sauropsida with those of 
Mammals shows that t-he levator hyoidei — from which in 
Amphibia and Sauropsida the depressor mandibulae is derived 
— preserves in Mammals, and especially in Monotremes, its 
primary condition as a muscle affixed to the hyoid bar. 
The above considerations support the theory of Fiirbringer 
that the change of jaw-joint was associated with the develop- 
ment of the mammary function: “Dieses Abweichen der 
Mammalia von dem fortschreitenden Entwickelungsgange, 
wie ihn Amphibien und Sauropsiden einschlagen, legt den 
Gedanken nahe, dass bei ihnen in jugendlichen Entwicke- 
lungsstadien, in den Beuteljungenkindheit, ein den Sauge- 
thieren eigentiimlicher ausserer Anstoss eintrat welch er zu 
dieser Lockerung des Unterkiefers Veranlassung gab. Ich 
neige dazu, diesen in der saugenden Tatigkeit der Beutel- 
jungen zu erblicken. Wie bei den Anurenlarven nur der 
vordere Teil des zu einiger Selbstandigkeit gestalteten 
Unterkiefers zum Anheften und Kaueu verwendet wurde, so 
dient auch bei den maminalen Beuteljungen nur der vordere 
Abschnitt der Mandibula der Saugfunction, welche zusammen 
mit der Ausbildungder Milchdriiseneine neue Erregungsschaft 
gegeniiber alien Nicht-Saugetieren ist.’’ 
- Some of the muscle-phenomena appear to be secondary to 
the change of jaw- joint. The pterygo-tympanicus of Dasyurus 
and higher Mammals becomes transformed into the tensor 
