630 
F. H. EDGEWORTH. 
MS in B V a d y p u s in a r m o r a t u s, Das y pus n o v e in c i n c t a^ 
Choloepns didactylus j and (3) to the part of the dorsal 
]iortion of a hyoid ventral constriction which is inserted into 
tlie stylo-hyal, as in the pi^. 
The name stylo-hyoidens was applied by Owen and by 
3'oldt to (2) above,, and also by Toldt to the hyoid ventral 
constrictor of Monotremes. 
On the Homologies of the Posterior Digastric 
Muscle in X o n - M a m m al s . — According to Gegenbanr and 
Huge the posterior digastric is homologous with the depressor 
mandibulte of lower vertebrates, and the latter thought that 
the change of insertion, from mandible to hyoid, was related 
to the formation of the new squamoso-mandibular joint. 
Filrbriiiger and Bijvoet rejected this theory, the former 
being of opinion that the old depressor mandibulae was either 
altogether gone or would be found as a rudimentary structure 
attached to the malleus, the latter finding it difficult to under- 
stand how the insertion of a depressor mandibulae should be 
transferred to the hyoid. 
BijvoePs theory was that the posterior digastric is derived 
from a ventral constrictor of the hyoid segment, and is serially 
homologous with the intermandibularis s. mylohyoid of the 
mandibular segment. This becomes all the more probable 
from the investigations detailed in this paper, which show 
that the primary upper attachment of the muscle is to the 
hyoid bar. 
The serial homology is well brought out in fig*. 4, which, 
being drawn from a slightly oblique section of Dasyurus in 
stage B, shows the posterior digastric on one side and the 
intermandibularis on the other. 
On the Homologies of the Stapedius in Non- 
Mammals. — Fiirbriuger was of the opinion that the de- 
pressor mandibulm of non-mammals has entirely disappeared 
in mammals, or will be found as a rudiment attached to the 
malleus — the hind end of the primitive jaw. No such rudi- 
ment, however, was found in the embryos investigated. 
Gaupp stated that the disappearance of the depressor is a 
