THE MANDIBULAli AND HYOID MUSCLES OF MAMMALS. 613 
111 stage C (figs. 7 — 10 and 12) the stapes^ has chondrified. 
Idle crista parotica is beginning to form, as a sliglit down- 
ward extension from the chondrified portion of the enter 
wall of the anditory capsule. It is deepest in front, where 
the latero-hyale is attached, and gradually lessens behind. 
The stapedius muscle, taking origin from the lower edge of 
the crista parotica, passes forwards and downwards to the 
hyoid bar below the interhyale. The upper end of the 
posterior digastric — attached solely to the hyoid bar in stages 
A and B — has now an additional origin, by a long tendon 
passing upwards behind the hyoid bar to the paroccipital 
process. 
In stage D (fig. 19) chondrification has extended from the 
middle portion of the hyoid bar into the latero-hyale, the pars 
inter-hyalis remaining precartilaginous. The origin ^ the 
stapedius muscle has shifted still further inwards, the muscle 
arising’ from the floor of the fossa stapedii ; it is inserted into 
the hyoid bar below the inter-hyale. 
In stage F the inter-hyale has disappeared, and the car- 
tilaginous latero-hyale and stylo-hyale, but for a small nodule, 
are replaced by a ligament which, ventrally, is continuous 
with the cartilaginous hyoid cornu of the hyoid apparatus. 
The insertion of the stapedius has shifted inwards to the 
stapes. 
In stage H the attachment of the posterior digastric to the 
hyoid bar is lost ; its attachment to the paroccipital process 
is tendinous up to stage J — the latest investigated — but in 
the adult it has a fleshy origin. 
The condition of the stapes, stapedius and posterior digastric 
muscles of 10 mm. specimens of Didelphys aurita is similar 
to that of the Dasynrus in stage H. 
The anterioi’ digastric is proliferated from the hinder part 
of the intermaudibularis in stage D (fig. 18). The fibres are 
given off from the ventral surface of the posterior portion of 
the muscle and are directed transversely outwards', and have 
1 A stapedial artery passes through the stapes in stages A-C ; it dis- 
appears subsequently. 
