574 
F. H. EDGP]WOETH. 
the form of au inverted the two limbs of which lie on 
either side of the lower jaw. The temporal mnscle develops 
from the upper limb^ the masseter from the lower externnl 
limb^ and the two pterygoids from the lower internal limb. 
He did not mention the tensor tympani or the tensor veli 
palatini. Eschweiler described the development of the tensor 
tympani and tensor veli palatini in the pig. He found the 
first indication of the muscles in embryos of 15' 75 mm. 
Scheitel-Steisslange, when the masticatory musculature 
appears in the Blastemsaule which contains MeckeFs 
cartilage as its nucleus. The Anlagen of the tensor tympani 
and the malleus portion of MeckeFs cartilage form at first an 
indivisible mass. The differentiation of the muscle- Anlage 
to muscle occurs in embryos of 20*5 mm. It forms the aboi-al 
end of the ^^Blastemsaule/’whiclE orally, forms the masticatory 
muscles. On the medial side of the Anlage of the maaticatory 
muscles develops the Anlage of the tensor veli palatini ; its 
aboral end is gradually lost in connective tissue, which is con- 
tinuous, aborally, with the Anlage of the tensor tympani (i. e. 
the two muscles do not overlap). The Anlage of the tensor 
tympani shifts aborally, whilst its development into muscle 
takes place in the reverse direction. In later development 
the oral end of the tensor veli palatini spreads into the velum, 
and the tensor tympani gains an attachment to the labyrinth 
capsule. 
Lewis (1910) gave an account of the development of the 
masticatory muscles in man, which is very similar to that given 
by Reuter iu the pig. The chief point in which he differed is 
that ‘‘iu a 14 mm. embryo the Mm. tensor tympani and tensor 
veli palatini are to be recognised and are connected with t he 
ptyerygoid mass from which they probably arise.^^^ 
In the following account of the development of the man- 
dibular and hyoid muscles, those of the mandibular segment 
are first described and subsequently those of the hyoid 
segment. On account of the relationship of the anterior 
digastric to the posterior digastric, it is convenient to consider 
the depressor mandibulee anterior and anterior digastric 
