G34 
F. H. EDGEWORTH. 
posteriores^ e. g. Canis (Chaine), or by a more distal branch 
than that tor the posterior digastric^ - Tatiisia^ Marsupials 
(Bijvoet). 
Two views have been advanced as to the derivation of the 
muscle. Chaine held that it is homologous with the depressor 
mandibulgeof lower Vertebrates; Fiirbringer and Bijvoet that 
it is a derivation of the facial musculature. The above- 
described phenomena in Dasyurus prove the correctness of 
the latter theory; they show that it is derived from the 
platysma. The muscle is one which was identified by some 
observers as a single-bellied digastric inserted into the lower 
jaw, e. g. in Dasyurus, Tatusia, Manis. This question is- 
discussed above (pp. 627, 628). 
On the Derivation of the Muscles of the External 
Ear. — The comparative anatomy of the muscles of the external 
ear in Mammals has been investigated by Huge, Baum and 
Kirsten, and by Boas and Paulli; their development by Killian, 
Dobers and Futamura. 
Euge was of the opinion that all the auricular muscles 
were derived from the platysma ; none from the sphincter 
profundus. 
Boas and Paulli agreed with this opinion, except in regard 
to the depressor auris, which they described as the pars 
auricularis of the sphincter profundus. 
Killian stated that the muscles in front of the ear — 
attraheus, attolens (anterior part), helicis major, helicis 
minor, tragicus — were derived from an upgrowth of the 
platysma in front of the ear; and those behind — retrahens, 
hinder part of the attolens, obliquus, transversus — from the 
hinder superficial layer of the dorsal portion of the hyoid 
arch musculature. 
Dobers stated that in the pig the muscles develop from two 
groups which “ zwar gemeinschaftlicher Abstammung sind, 
sich jedoch sehr fruhzeitig trennen.^^ One group lies from 
the very beginning caudo-dorsal to the ear; the second group 
lies more ventral, and can be called the embryonic platysma,. 
for it also gives rise to the platysma myoides. 
