THE MANDIBULAR AND HYOID MUSCLES OF MAMMALS. 603 
two heads from the alispheiioid, in Tatusia by two heads, one 
from the alisphenoid, the other from the alisphenoid and 
palate bones, in Taman dua by two heads, one from the 
parietal, the other from the palate. 
The first insertion of the external pterygoid is into the 
condylar process of either the ossified mandible (Dasyurus) 
or its Anlage (rabbit and pig) . There is no transitory insertion 
into MeckeTs cartilage. The development of a condylar 
process is synchronous with the development of the external 
pterygoid. These phenomena support the view of Gaupp that 
the condylar process is primarily a Muskelfortsatz.^^ 
An external pterygoid muscle is present in most Mammals. 
Two exceptions have been recorded and are of considerable 
interest. Leche was of opinion that the internal and external 
pterygoid muscles auf eiuen gemeinsamen Ursprung zuriick- 
gefuhrt werden konnen,^’ but did not record any instances 
other than that of Phoca, in which one muscle only was present, 
which might represent a common muscle mass from which in 
other Mammals internal and external pterygoids were 
differentiated. 
Humphry had described in Phoca communis one ptery- 
goid muscle only arising from the outer side and edge of the 
slightly developed pterygoid part of the sphenoid and passing 
to the inner side of the angular part of the jaw.^^ He did not 
mention its innervation nor did he describe the temporal muscle. 
I find that iuHalichoerus grypus (grey seal) the masseter, 
zygomatico-mandibularis, temporal, external pterygoid, in- 
ternal pteryg’oid, tensor veli palatini and tensor tympani 
muscles are present. The temporal is inserted into the coronoid 
process, the external pterygoid into the condyloid process 
and interarticular meniscus, and the internal pterygoid into 
the inner side of the angular part of the jaw. The ramus 
lateralis of the mandibular division of the trigeminal nerve 
supplies the masseter, zygomatico-mandibularis, temporal (by 
three twigs), and the external pterygoid ; the ramus medialis 
supplies the internal pterygoid, tensor veli palatini, and tensor 
tympani. 
