612 
F. H. EDGEWORTH. 
]) 0 ssessed internal pterygoid, a nmscle representing the 
pteryg’O-tyinpanicus and tensor tympani (derived from the 
medial muscle) ; temporal and detrahens mandibidae (derived 
from the lateral muscle) ; but not external pterygoid, rnasseter, 
zygomatico-mandibularis, or depressor mandibulae anterior. 
Muscles of the Hyoid Segment. 
Tn stage A ot‘ the Dasyurus (fig. 3) the hyoid apparatus 
consists of liyoid and first branchial bars and a basibranchial. 
There is no basdiyal. The ventral ends of the hyoid and first 
branchial bars are continuous with the basi-branchial. The 
hyoid bar forms a continuous structure — of stapes, inter-liyale, 
and stylo'hyale ; the latero-hyale extends upwards from the 
interhyale to the auditory capsule. There is as yet no crista 
parotica. The only chondrified parts of the hyoid bar are 
the extreme lower end and the middle part ; to the latter are 
attached the stylo-pharyngeus on the inside and the upper 
end of the posterior digastric on the outside. The posterior 
end of the stylo-glossus is attached to the tendinous part of 
the hyoid bar just below the middle cartilaginous part. The 
branchio-hyoid passes from the first branchial to the hyoid bar. 
The adjacent ends of the genio-hyoid, omo-hyoid and sterno- 
hyoid are attached to the first branchial bar. The thyro-hyoid 
is not yet developed. There are two hyoid muscles — the 
stapedius and posterior digastric. The former nrises from 
the outer chondrified wall of the upper part of the auditory 
capsule and passes downwards and forwards to be inserted 
into the back of the upper part of the stylo-hyale. The 
posterior digastric takes oi'igin from the middle chondrified -- 
portion of the hyoid bar, and passes downward and forwards 
outside the bar to a transverse tendon connecting the muscle 
to its fellow just behind and slightly underlapping the inter- 
mandibularis. No trace of the anterior digastric or of the 
Anlage of the sphincter profundus and platysma is visible, 
fidie N. facialis passes backward on the external surface 
of the stapedius and then downwards on the external surface 
of the posterior digastric. 
