604 
F. H. f:i)GEWOIITH. 
In Phoca communis s. vitulina (common seal) there 
is one pterygoid muscle only^ as described by Humphry; it 
agrees in form, origin, insertion and innervation from the 
ramus medialis, with the internal pterygoid of Halichoerus. 
The temporal is inserted into the interarticular meniscus, 
the neck of the condyloid process and the coronoid process 
(fig. 44) ; it is innervated by four twigs from the ramus 
lateralis. 
It is clear that the ‘'HemporaP^ of Pboca represents the 
temporal + external pterygoid of Halichoerus, and the condi- 
tion is probably due to non-separation of these two muscles 
— a persistence of an embryonic stage. 
The matter, however, is complicated by the statement of 
Toldt that in Phoca vitulina both pterygoid muscles exist — 
a statement which does not agree with the findings of Humphry 
and myself in Phoca vitulina, though it does agree with 
what I found in Halichoerus grypus. 
In Manis tetradactyla, according to Lubosch, there is 
only one pterygoid muscle arising from the palate bone and 
passing down internal to the N. mandibularis. No separate 
external pterygoid was found. Lubosch was of the opinion that 
er mit dem inneren Flugelmuskel verschmolzen ist, und ich 
beziehe die occipitalsten Pasern seiner Ansatzes, die in der 
Figur an den Condylus tretend gezeichnet sind, aiif ihn.^’ 
I found a similar condition in Manis pentadactyla. 
The above-described observations show that the Anlage of 
the masticatory muscles in Mammals divides into medial and 
lateral portions. From the medial portion or muscle are 
developed the internal pterygoid, pterygo-tympanicus or 
tensor veli palatini, and the tensor tympani. From the lateral 
portion or muscle are developed the temporal, masseter, 
zygomatico-mandibulai-is, and external pterygoid. 
These phenomena of development are in harmony with, 
and offer an explanation of, the method of innervation by the 
mandibular division of the fifth nerve. The muscles developed 
from the medial portion are innervated by the ramus medialis, 
those developed from the lateral portion by the ramus lateralis. 
