576 
F. H. EDGEWOFTH. 
internal pterygoid, the latter tlie common Anlage of the 
tensor veli palatini and tensor tympani. The internal ptery- 
goid retains its origin from the ala temporalis, whilst the upper 
end of the Anlage of the tensor veli palatini and tensor 
tympani has grown inwards beneath the ala temporalis and 
is attached to the (mammalian) pterygoid bone, which has 
now developed behind and in continuity with the palatine 
bone. The coronoid process of the mandible is beginning to 
form, and the insertion of the lateral muscle has spread down 
a little on its outer side. Cells proliferated downwards and 
backwards from the anterior of these muscle-fibres on the 
outside of the mandible form the beginning of the masseter 
muscle (fig. 6). 
In stage D (figs. 14 to 18) a cartilaginous bar — the 
processus ascend ens alae temporalis — has appeared, extending 
from the upper lateral edge of the ala temporalis to the orbito- 
parietal commissure ; it is a cartilaginous thickening of the 
anterior edge of the membrana obturatoria covering in the 
spheno-parietal foramen. The Anlage of the tympanic bone 
has appeared as a straight rod external to the hinder part of 
Meckehs cartilage; its anterior end is overlapped by the 
posterior end of the mandible. The origin of the lateral 
muscle — hitherto confined to the orbito-parietal commissure — 
has now additionally spread downwards, so that the muscle 
arises from orbito-parietal commissure, the membrana obtura- 
toria and the processus ascendens. The coronoid process of 
the mandible has extended further upwards and the inner 
fibres of the lateral muscle are attached to its medial side. 
The Anlagen of the squamous and malar bones are formed, 
and the masseter in part arises from them. The anterior 
digastric is being proliferated from the hinder part of the 
i nterm an dib u 1 aris . 
In stage E (figs. 20 and 21) a condylar process has formed 
as a slight elevation of the hinder end of the upper edge of 
the mandible; and the external pterygoid muscle, of which 
there is no trace in stage D, is differentiated from the lower 
posterior edge of the lateral muscle. It consists of muscle- 
