THYNG: SQUAMOSAL BONE. 
391 
3. Its relations to the chorda tympani are those of the quadrate, 
and negative the view that it can be either a part of the Sauropsidan 
columella or the hyomandibula of lower vertebrates. 
4. Its articulation with the malleus is of the same kind as that 
most common between the quadrate and the articulare in the non¬ 
mammalian vertebrates. 
The only important papers dealing with these homologies since 
that of Kingsley are those of Gadow (: Ola) and Broom (: 01; : 04). 
Gadow believes that the quadrate of the lower vertebrates is trans¬ 
formed into the tympanic of the mammals, a view for which he ad¬ 
vances no adequate evidence and which is open to many insuperable 
objections. Gadow also tries to overthrow the arguments of Kingsley 
and Gaupp, derived from the relative position of bones, gill clefts, 
and nerves by supposing that these may shift so that an element which 
is behind a gill cleft in one group may be homologous with one lying 
in front of the same cleft in another, and that nerves may slip around 
the various arches in a similar manner. Reply to such views is scarcely 
possible; reference may be made to Broman (’99, p. 650). 
Broom regards the quadrate as being transformed into the inter- 
articular cartilage found in the glenoid fossa of many mammals but 
the development of this is such as to preclude any such view, while 
the arguments as summarized by Kingsley and Gaupp for the incudo- 
quadrate homology render Broom’s interpretation extremely improb¬ 
able. 
If, then, the incus be the homologue of the quadrate (and until 
more convincing adverse evidence than that already at hand is pre¬ 
sented, most morphologists will continue so to regard it) it follows 
that association with the quadrate and otic capsule rather than jux¬ 
taposition with the parietal will be the most weighty evidence in 
ascertaining the homologue of the squamosal in the non-mammalian 
vertebrates. 
Cuvier carried his homologies into the lower vertebrates by way 
of the crocodiles, turtles, and lizards, and thence to the lower forms; 
and his conclusions have doubtless had great weight with all who have 
followed him. But this line is apt to lead (indeed has led) to erroneous 
conclusions. It would rather seem that we should follow the lines 
of descent. 
According to all who have dealt with the subject of mammalian 
ancestry, this group has descended from either the reptilian group 
