590 
F. H. EDGEWORTH. 
nerves pass between the internal and external pterygoids, 
then separate; the lingual is joined by the chorda tympani 
medial to the internal pterygoid and passes to the inferior 
maxillary ganglion ; the inferior dental passes forward on the 
medial surface of the Anlage of tlie mandible. The mylohyoid 
branch of the inferior dental passes downwards between 
Meckehs cartilage and the Anlage of the mandible and then 
forwards on the lateral surface of the intermandibularis muscle. 
^Jdie auriculo-temporal passes outwards between Meckel’s car- 
tilage and the Anlage of the mandible. 
In a 24 mm. pig embryo the condyloid and coronoid pro- 
cesses of the mandible are better marked, and ossification has 
begun. The upper end of the temporal has grown further 
upwards outside the membranous cranium, but is not attached 
to the orbito-parietal commissure. The Anlage of the parietal 
bone is not yet formed. The Anlage of the zygomatico-man- 
dibularis and masseter arises partly from the temporal, partly 
from the Anlage of the zygomatic arch. 
In a 32 mm. embiyo (fig. 64), the orbito-parietal commis- 
sure is complete ; it is covered by the Anlage of the parietal 
bone. The alisphenoid bone is not yet formed. The temporal 
arise^ from the parietal bone and the lamina ascendens alas 
temporalis which is now formed. The Anlage of the zygo- 
matico-mandibularis and masseter is beginning to separate 
into those two muscles. The internal pterygoid remains single, 
arising from the under surface of the ala temporalis. The 
proximal end of the tensor veli palatini has spread into the 
soft palate round the hamulus ; its distal end is connected with 
the tensor tympani by a tendinous intersection. 
The above-described phenomena show that the Anlage of 
the masticatory muscles in Mammals divides into medial and 
lateral portions, and that each develops into certain muscles. 
These may be taken separately. 
Medial Muscle. — The primitive form of the medial 
muscle is present in 8'5 mm. embryos of Ornithorhynchus 
and stages A and B of Dasyurus, taking origin from the ala 
temporalis and inserted into the whole length of Meckel’s 
