THE .MANDIBULAR AND HYOID ^FUSCLES OF MA.MMAF.8. 635 
From tlie second group develop tlie tragicus^ adductor 
auris inferior and externus and helicis major; from the first 
group the other muscles. 
Futamura’s statements differ much from the above ; they 
are thaF in the pig, the scutularis, helicis major and minor 
are developed from the platysma, and the other muscles from 
the sphincter auris, whicli is derived from the sphincter colli. 
In Dasyurus the superficial muscle sheet spreads upwards 
from the site of its formation in the mesoblast external to 
the hyoid ventral constrictor, and divides into two layers, 
each consisting of embryonic muscle-cells easily distinguish- 
able from one another and from surrounding mesoblast. 
I'he sphincter profundus does not spread above the zy^gomatic 
arch, nor is it present behind the ear. Only the depressor 
auris is developed from the sphincter profundus ; all the other 
muscles are derived from the platysma sheet. ^Jdiis method is 
also evident in Didelphys aurita. The embryological 
phenomena in these two Marsupials thus confirm the theory 
of Boas and Paulli. 
The development of the cervical portion of the platysma 
by gradual descent from the hyoid region is of special interest 
owing to the discovery by Kohlbrugge that in many Marsu- 
pials and Edentates ^ the R. cervicis of the X. facialis is 
entirely replaced by the Xn. cutanei of the cervical nerves 
so that it is entirely restricted to the face. Kohlbrugge ad- 
vanced the following theories in explanation: ‘Milntweder 
tauscht der R. colli des Menschen nur eine primitive Lage vor 
und erreichte die Halsregion nur durch ein Herabrucken der 
Muskulatur welches bei den Marsupial ieren danu noch uicht 
bei den Monotremen wohl eingetreten ware, oder wir niiissen 
eine secundiire Reduction dieser Theile bei Marsupial iern 
(und Manis) annehmen, die Gegend welche sonst derFacialis- 
muskulatur angehorte ware danu von den spinalen Xerven 
und ihrer Muskeln erobert worden.” He was inclined to 
accept the latter theory. 
1 Cnsciis orientalis, Ciiscus macnlatus, Paradoxnrus her- 
iiiaphrodita, Macropus bruiiii, Manis javaniea. 
