628 
F. II. EDGEWORTH. 
extending fi*om mastoid process to angle and lower margin 
of jaw.^^ Snbsecpiently, Chaine stated that an lieu dn 
muscle qne signale Humphry j’ai trouve une formation rni- 
tendineuse mi-muscnlaire qui parassait en tenir lieu/^ 
probably, therefore, an auriculo-mandibularis ; and he also 
depicted, though not describing, an additional muscle named 
digastric. 
It is not known whether a true posterior digastric exists 
in Cyclothurus and Chlamydophorus. In the latter a small 
muscle passing from the bulla tympani to the mandible was 
found by Macalister, but not by Hyrtl. 
The case of Tamandua is considered above (p. 621). 
The existence of a monogastric muscle homologous with the 
posterior digastric and inserted into the lower jaw is thus 
very doubtful. The instances which have been described are 
probably cases of an auriculo-mandibularis — which is derived 
from the platysma (vide pp. 632, 634). 
On the Primary Form of the Stapedius Muscle 
in Mamm al s. — The stapedius muscle in early post-embryonic 
stages of Dasyurus arises from the outer surface of the 
auditory capsule and is inserted into the upper part of the 
stylohyale, forming a levator hyoidei. Its origin subsequently 
shifts to the lower edge of the developing crista parotica, and 
then to the floor of the fossa stapedii, whilst its insertion 
shifts to the stapes. The initial stage present in Dasyurus 
is, in part, passed over in the rabbit and pig, for in them 
the first dorsal attachment of the muscle is to the floor of the 
fossa stapedii; on the other hand, its first ventral attachment 
is to the upper end of the stylo-hyale, subsequently shifting to 
the inter-hyale and then to the stapes as in Dasyurus. The 
shifting of* insertion from the inter-hyale to the stapes takes 
place with the disappearance of the inter-hyale in all three 
animals. The primary form of the stapedius as a levator 
hyoidei is present in 8'5 mm. embryos of Ornithorhynchus, 
and in stage 47 of Echidna, and in them persists into adult 
life. It is the muscle which was termed mastoideo-hyoideus 
by Schulman and Bijvoet. 
