THE MANDIEULAli AND HYOID MUSCLES OE MAMMALS. 589 
giving off the rami medialis and lateralis, and then forwards 
in the gap between the two limbs, dividing into auriculo-tem- 
poral, mylohyoid, inferior dental, and lingual branches. 
Figs. 59-63 and 72, 73 are made from a 21 mm. pig embryo. 
The stage of development of the masticatory muscles is slightly 
more advanced than that of a 16 mm. rabbit embryo. The ala 
orbitalis is continuous posteriorly with the orbito-parietal 
commissure, which does not reach the parietal-platte. The ala 
temporalis is just beginning to chondrify. The processus 
alaris is not yet formed. The Anlage of the mandible, in 
which ossification has not begun, lies outside MeckePs cartilage 
and shows slightly marked coronoid and condylar processes. 
The Anlage of the masticatoiy muscles has divided into medial 
and lateral portiotis. The former consists of internal ptery- 
goid, tensor veli palatini and tensor tympani — which are 
separate structures, though very close together. The internal 
pterygoid arises from the ala temporalis and is inserted into 
the mandible, the spindle-shaped cells not having any attach- 
ment to MeckePs cartilage. The tensor veli palatini, which 
is not attached to any skeletal structure, lies internal to the 
upperend of the internal pterygoid, with its muscle-cells at right 
angles to those of the internal pterygoid. The tensor tympani 
lies behind the tensor veli palatini, with a free anterior ex- 
tremity ; it is inserted, posteriorly, into the non-chondrified 
malleus portion of Meckel’s cartilage. The lateral portion of 
the Anlage of the masticatory muscles consists of temporal 
external pterygoid, zygomatico-mandibularis, and masseter 
muscles, which are only partially separated from one anothei*. 
The temporal has no upper attachment, its lower anterior 
fibres are in front of the external pterygoid, those above 
extend upwards outside the Gasserian ganglion ; it is inserted 
into the coronoid process of the mandible. The external 
pterygoid arises from the ala temporalis and is inserted into 
the condylar process of the mandible. 
The Anlage of the zygomatico-mandibularis and masseter is 
continuous with the temporal and is inserted into the Anlage 
of the mandible. The united lingual and inferior dental 
