622 
F. H. EDGEWOKTH. 
A sterno-mandibularis may occur with either condition^ ^ - R- 
with an undivided hyoid ventral constrictor in Toly pent es 
tricin ctus and Dasypus villosus, with a divided one in 
D a s y p u s n o v e m c i n c t a , Myrmecophaga and Tainand ua. 
In the pig, as described above, the hyoid ventral constrictor 
divides into dorsal and ventral portions. The dorsal portion 
separates into two muscles — the jngulo-hyoideus and the pos- 
terior digastric. The jugulo-hyoideus is inserted into the stylo- 
hyal. The ventral end of the posterior digastric unites with the 
posterior end of the anterior digastric and forms the digastric 
muscle. The ventral portion of the hyoid ventral constrictor 
becomes the stylo-hyoid ; it arises from the stylo-hyal and 
passes to a ventral aponeurosis uniting it with its fellow, and 
also gains an insertion to the side of the first branchial 
cartilage. 
In the rabbit the sequence of events is, but for two differ- 
ences, the same. The jngulo-hyoideus gains an insertion to 
the first branchial cartilage, becoming the jugulo-branchialis. 
The ventral portion of the constrictor becomes the stylo-byoid 
and is inserted into the basibranchial ; the ventral aponeurosis 
disappears. 
In both animals the posterior digastric becomes tendinous 
and has no nerve-supply, but in the embryo a branch of the 
X. facialis nerve passes to it. 
On the Formation of the Anterior Digastric 
Muscle. — Consideration of the adult form and innervatioti 
of the anterior digastric muscle led Gegenbaur, Huge, Fiir- 
bringer, Schulman and Bijvoet to the opinion that it is 
derived from the intermandibularis s. mylo-hyoid, and the ob- 
servations of Kallins, though he did not observe the earliest 
stages of the process, tended to confirm this view. Chaine 
stated that the digastric muscle is due to longitudinal division 
of a muscle extending from the sternum to the mandible into 
inner and outer portions, the inner forming thegenio-hyoid and 
sterno-hyoid, the outer the digastricus. 
Futamura stated that in man and pig the anterior digastric 
is due to a forward extension to the jaw of the muscle blastema 
