MORPHOLOGY OF THE VERTEBRATE SKULL 29 
as in modern snakes, chameleons, tortoises and some urodeles 
(Kingsbury and Reid) and caecilians (Kingsley). If, as now 
appears probable, the stapes touched the quadrate in Cynodonts, 
then it is clear that stapes, quadrate, articular, already formed a 
connected train of bones (fig. 23). Thus would be met Gadow’s 
objection (88) that “ . . . . the incus cannot be the 
homologue of the quadrate because of the impossibility of inter- 
calating the quadrate as an incus into the ossicular chain as a 
link between the stapes (hyomandibula) and lenticulare (sym- 
pletic) and the malleus (articulare).’”’ But the quadrate (incus) 
was not ‘intercalated’ in the chain; it was there, from the time 
that the hyomandibular (stapes) became attached to it. 
Very obscure and difficult is the complex of questions involv- 
ing the origin of the handle of the malleus, of the tympanic 
membrane and tympanic bone (annulus tympanicus), the fate 
of the reptilian extracolumella and angulare. 
In typical reptiles the tympanic membrane is stretched on or 
near the quadrate, squamosal and articular. Between the inner 
and outer layers of the tympanic membrane is inserted the extra- 
columella (fig. 20), which is joined to the true stapes; this extra- 
columella, like the stapes itself, is believed to be a derivative of 
the hyoid arch; from the extracolumella springs a dorsal process, 
the suprastapedial, or intercalare; the ascending hyoid is gen- 
erally attached either to the extracolumella or to the parotic 
process of the opisthotic. In mammals the handle of the malleus 
(manubrium mallei) is inserted into the middle layer of the 
three layered tympanic membrane; the extracolumella, if pres- 
ent, is not recognized as such and is not connected with the 
stapes; the hyoid is attached to the periotic. 
Kingsley (?00) held that the malleus is a compound element, 
that the manubrium (fig. 21) in ontogeny arises ‘‘distinct from. 
the body of the malleus, that it is at first, like the extracolumella 
a separate element developing in the tympanic membrane and 
only later uniting with the rest of the structure.”’ Kingsley 
therefore concluded that the manubrium mallei had been derived 
from the extracolumella of the reptilian ossicular chain, a view 
endorsed also by Fuchs. Hammar and Fuchs have also found 
