036 
F. H. EDGEWOETH. 
There is a third possibility — that the superficial muscles of 
the neck may be of facial origin and receive a secondary 
innervation by cervical nerves ; this is confirmed by the de- 
velopmental phenomena in Dasyurus, where the platysrna 
originates in the hyoid region and spreads down the neck. 
This phenomenon is one which can be assimilated with 
others occurring in the muscles of the head. I have previously 
given a list of thirteen in various Vertebrates, which appear 
to be referable to the law that if a muscle grows into one or 
more neighbouring segments, that portion tends to be inner- 
vated by the corresponding nerve or nerves. 
It is noteworthy that in Monotremes (McKay, cited by 
Kohlbrngge) the cutaneous muscles of the neck are innervated 
by both the K. facialis and the first four cervical nerves — i. e. 
a condition exists re innervation intermediate between that 
present in Marsupials and that in which the innervation is 
solely by the seventh nerve. It is similar to the double inner- 
vation of the trapezius by the N. accessorius and cervical 
nerves. 
Kohlbrugge also found that in Marsupials the cervical 
nerves innervate the Platysma sheet in front of the ear, the 
N. facialis only innervating the sphincter profundus. The 
cervical nerves thus spread beyond their segmental territory 
and innervate muscles which did not originate in it. This 
must be a very rare occurrence as regards motor nerves, 
though it is parallelled by the N. vagus. 
On the Homologies of the Sphincter superficial is 
s. colli, Platysma, and Sphincter profundus, in N on- 
M am mads. — Rnge, who investigated the adult form of the 
hyoid muscles in all classes of Vertebrates, stated that the 
sphincter colli of Monotremes is homologous with the muscle 
Covd of Selachians, and the Platysma group with the muscle 
Cgind. 
Now in Ornithorynchus, Dasyurus and pig these muscles 
are formed from a common Anlage developed in the mesoblast 
outside and not as an extension backwards of the hyoid 
ventral constrictor — so that the homologies suggested by Rnge 
