618 
F. H. EDGEWORTH. 
a 32 mm. embryo (fig. 64) the ventral end of .the lower part 
of the original hyoid constrictor has gained an insertion to 
the external surface of the first branchial cornu, though 
keeping its transverse aponeurosis to the muscle of the 
opposite side — a stylo-hyoid muscle is thus formed. 
The developmental phenomena in the rabbit are, for the 
most part, similar to those in the pig. The anterior digastric 
is proliferated from the intermandibnlaris,and grows backwards 
medial (not lateral, as in the pig) to the hyoid ventral con- 
strictor. The latter divides into dorsal and ventral portions, 
the dorsal of which separates into posterior digastric and 
jugulo-branchialis, whilst the ventral forms the stylo-hyoid. 
The jngulo-branchialis becomes inserted into the first branchial 
cornu; and the stylo-hyoid into the basibranchial, losing its 
ventral transverse aponeurosis. The posterior digastric 
becomes tendinous. 
On the Primary Form of the Posterior Digastric 
in Mammals. — BijvoePs conclusion, from an examination of 
the adult condition of the stylo-hyoid and posterior digastric 
in many classes of Mammals, was that, primitively, sichvom 
Schadel zum Znngenbein, oder besser zn eicer Bindegewebs- 
lager, das sich ventral am Hyoid heftet, eine Muskelmasse 
erstreckt, die vom N. facialis innerviert wird.^^ “ Den hier 
beschriebenen Znstand begegnen wir bei Echidna und 
Ornithorhynchus. Der M. styloideus reprasentiert die einheit- 
liche Muskelmasse, welche vom Schadel entspringt und die 
ventrohyoi deale Bindegewebsmasse sich festheftet.’’ 
The developmental phenomena in Ornithorhynchus, 
Echidna, Dasyurus, pig, and rabbit show that a still more 
primitive condition of the muscle is one in which it is attached 
dorsally to the hyoid bar and passes ventrally to a transverse 
aponeurosis, forming a hyoid ventral constrictor or inter- 
hyoideus. This condition in Dasyurus, pig and rabbit is 
succeeded by one in which the muscle loses its dorsal attach- 
ment to the hyoid bar, and, extending dorsally, gains a new 
one to the skull — to either the paroccipital or mastoid process. 
The more primitive condition, however, persists in Echidna, 
