20 WILLIAM K. GREGORY 
5. The detachment of the anterior or dentary portion of the 
reptilian jaw from the posterior portion is a process for which 
analogies are offered among scarid fishes, Mosasaurs and Capri- 
mulgus. According to Gaupp’s view (pp. 657-658) this detach- 
ment has arisen in connection with a change in the muscular 
mechanism for the opening of the mouth. In reptiles, the jaw 
is depressed chiefly by the depressor mandibulae, which is finally 
lost in mammals. In mammals the jaw is depressed by the 
muscles of the floor of the mouth cavity, assisted by the external 
pterygoid muscles. An increase in size and strength of these 
muscles, which at first merely assisted the depressor mandibulae 
and which are all inserted in the dentary bone, would lead, 
thinks Gaupp, to the detachment of the dentary from the bones 
composing the hinder half of the jaw. The diminution of the 
depressor mandibulae muscle may, in turn, be ascribed to the 
reduction of the quadrate and to the transformation of the skull 
in the auditory region, under the influence of the rapidly 
enlarging brain. 
6. The secondary attachment of the ascending ramus of the 
dentary to the squamosal again finds its analogue among the 
searid fishes, where an ascending process of the dentary bone 
has formed a joint with the supramaxillary. The first step in 
this process in the ancestors of the mammals was probably the 
formation of a simple glandular cavity (Schleimbeutel) between 
the connective tissue on the lower surface of the squamosal and 
the connective tissue covering the ascending process of the den- 
tary (see paragraph (1) above) at the place where the external 
pterygoid muscle was inserted. The meniscus or interarticular 
dise (1911, pp. 659, 626-629) represents a separated portion of 
the connective tissue covering the condyle (Gaupp, Lubosch), is 
continuous with the fibers of the external pterygoid muscle and 
has nothing whatever to do with the quadrate (with which 
element Broom (’90) had sought to homologize it). 
The cartilaginous epiphysis (‘accessory cartilage’) of the con- 
dyle, which is very large in embryonic stages, is not a portion 
of the primordial chondrocranium, but is purely secondary, like 
the cartilaginous areas in many other dermal bones (Gaupp ’07). 
