THE MANDIBULAR AND HYOID MUSCLES OF MAMMALS. 599 
^Temporal. — In Dasyurus the first origin of the lateral 
masticatory muscle (from which the temporal, masseter, 
zygomatico-mandibnlaris and external pterygoid are sub- 
sequently formed) is from the orbito-parietal commissui*e ; 
the dorsal attachment of the muscle then spreads backwards 
to the parietal-platte and downwards to the membrana 
obtnratoria covering in the spheno-parietal foramen, with its 
front edge to the lamina ascendens of the ala temporalis. On 
the occurrence of ossification the temporal muscle, which has 
been formed owing to the differentiation of the lateral group 
muscles, arises from the parietal and alisphenoid bones, the 
former being developed over the orbito-parietal commissure 
and parietal-platte, the latter over the ala temporalis, lamina 
ascendens and the membrana obtnratoria. 
In the rabbit and pig, with a longer intra-nterine develop- 
ment, the Anlage of the lateral masticatory muscle separates 
into the muscles it forms before attachment takes place. The 
temporal becomes attached to the lamina ascendens alae 
temporalis, and spreads upwards to the territory of the orbito- 
parietal commissure and parietal-platte, but these latter 
structures are by that time covered by the Anlage of the 
parietal bone from which the muscle gains an origin. On the 
subsequent ossification of the alisphenoid bone the lower 
fibres arise from that bone. 
The lamina ascendens alae temporalis is complete in Dasyurus 
and Didelphysaurita; it has a free upper end in rabbit, 
pig, and Dasypus. The orbito-parietal commissure is complete 
in all four animals. 
The lower end of the lateral masticatory muscle in the just 
born Dasyurus is at first attached to the upper edge of 
MeckePs cartilage via a mass of cells in which the Anlage of 
the mandible is just visible. Ossification subsequently 
extends upwards forming a coronoid process and downwards 
on the lateral side of MeckePs cartilage ; in relation with 
these changes the insertion of the muscle becomes forked and 
laps the coronoid process on both sides, though to a greater 
extent laterally than medially. 
VOL. 59 , PART 4 .— NEW SERIES. 
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