620 
F. FI. EDGEWORTH. 
- The hyoid ventral coustrictor or styloideus muscle, uncon- 
nected with the anterior digastric to form a digastricus, passes 
downwards to a ventral aponeurosis connecting it with its 
fellow below the basibranchial and ventral ends of the hyoid 
bars. This condition is present in stages A-D of Dasyurus, 
in 14 mm. embryos of the pig, and is preserved to the adult 
condition in Echidna and Ornithorhynchus (Schnlman), and 
in Manis. It is also present in some of those Edentates, i.e. 
D a s y p u s V i 1 1 o s u s, T o 1 y p e n t e s t r i c i n c tu s, an d T a t u s i a 
novemcincta (Toldt), in which a sterno-mandibularis exists. 
The latter muscle (vide p. 625) is formed by the union of 
the anterior digastric with the sterno-hyoid, and the trans- 
verse aponeurosis of the hyoid ventral constrictor s. posterior 
digastric lies dorsal to the longitudinal muscle. 
In some Edentates, e.g. Bradypus tridactylus, the 
anterior end of the sterno-hyoid is in part attached to the 
posterior edge of the transverse aponeurosis of the hyoid 
constrictor s. posterior digastric (Bijvoet). 
In some Edentates the hyoid ventral constrictor s. styloideus 
s. posterior digastric divides into dorsal and ventral portions, 
the former taking origin from the skull and inserted into the 
stylo-hyal, the latter arising therefrom and passing to a ventral 
aponeurosis. 
Thus in Bradypus tridactylus (Bijvoet) the posterior 
digastric arises from the mastoid process and passes to a 
ventral aponeurosis (fig. 40)^; whilst in Bradypus mar- 
moratus (fig.' 41) the muscle is divided into dorsal and 
ventral portions. The stapedius muscle is present. A similar 
condition was found in a 30 mm. embryo, though the separa- 
tion into dorsal and ventral portions was not cjuite complete. 
Toldt described the posterior digastric in Easy pus 
villosus as arising from the mastoid; its tendon broadens 
and unites with the posterior border of the mylo-hyoid. In 
Dasypus novemcincta (embryo 30 mm.) the posterior 
digastric is partly divided into dorsal and ventral portions, 
^ This figure of Bijvoet is reproduced for comparison with one of 
Bradypus marnioratu s. 
