THE MANDIBULAR AND HYOID ]\[USCLES OF MA:\LMALS. 577 
cells which are much smaller in size than those of the rest of 
the lateral muscle, and is probably proliferated from it, and 
not formed by cbauge of direction of already existing muscle- 
fibres. The external pterygoid muscle takes origin from the 
lower end of the ascending process of the ala temporalis and 
passes outwards to the condylar process of the mandible. The 
lower anterior fibres of the lateral muscle, which now forms 
the temporal, arise from the ascending process in front of 
the origin of the external pterygoid. 
In stage F (figs. 22 and 28) there is a downward and 
backward growth from about the middle of the tympanic bone. 
The goniale bone^ is also formed ; it lies dorsal-median to the 
tympanic bone, between it and Meckeks cartilage ; its anterior 
end extends slightly further forwards than does the tympanic, 
and its posterior end further back, underlappiug the malleus 
portion. The origin of the temporal muscle has extended 
backwards so that it additionally arises from the parietal- 
platte. The common Anlage of the tensor veli palatini and 
tensor tympani is beginning to separate into those muscles, 
and the insertion of the latter has shifted down the side of 
the malleus portion of Meckeks cartilage to its manubrial 
process. The tensor veli palatini is iiiserted on the inner side 
of Meckel’s cartilage and does not reach the tympanic bone 
lying on the other side of Meckel’s cartilage. Fig. 39, taken 
from a 10mm. specimen of Didelphys aurita, shows a little 
more advanced stage of the same condition. 
In stage H (figs. 24-27) the parietal bone is formed outside 
the orbito-parietal commissure and parietal-platte, and the 
temporal arises from it. 
The alisphenoid bone is formed on the outer and upper sides 
of the ala temporalis, and upwards round the processus 
ascendens, which is also involved in the ossification. The 
bone extends in front of and behind the process. The lower 
anterior fibres of the temporal, the external pterygoid, and 
the upper head of the internal pterygoid correspondingly 
^ I use Gaiipp’s nomenclature. Palmer has recently homologised it with 
the supra-angulare, though without any discussion of Gaupp’s views. 
