THYNG: SQUAMOSAL BONE. 
393 
bone supporting the tympanic membrane of the mammals (pi. 39, fig. 
1, Ty.) which is clearly without homology with this element. 
Gaupp (’94) studying the hammer-shaped bone in the temporal 
region of the Anuran skull found that it arose as a membrane bone 
primitively related to the quadrate and only secondarily extending 
upon the otic capsule (thus confirming Gegenbaur, '78, p. 481). He 
therefore called it the ‘paraquadrate’ a name which he suggested 
might eventually be replaced by the term ‘tympanicum.’ From the 
Anura he proceeded to the Urodeles and concluded that the same con¬ 
ditions prevailed for the bone which there covers the external surface 
of the quadrate. He therefore concluded that neither of these Am¬ 
phibian bones was homologous with the mammalian squamosal, since 
according to the information then available, the squamosal developed 
upon the otic capsule and was ‘parotic’ in character. While this con¬ 
dition may be true for the very specialized group of Anura it certainly 
does not hold for the Urodeles since there the element in question de¬ 
velops partly upon the otic capsule and partly upon the quadrate 
cartilage (c/. Kingsbury, : 03, p. 314). Besides, contrary to Gaupp, 
(if we accept the incus = quadrate homology), this element corresponds 
exactly with the mammalian squamosal, hence Gaupp’s term ‘para¬ 
quadrate ’ is merely a synonym of squamosal, so far as the Anura and 
Urodela are concerned, and is unnecessary. 
The Temporal Region in Caecilians. 
I have studied the development of the skull in Ichthyophis and fig¬ 
ure A shows the relations as they exist in the larval stage. It is at 
once evident that the area of the otic capsule which in Amphiuma is 
covered by the dorsal portion of the squamosal (pi. 40, fig. 4) is entirely 
without covering bones in the Caecilian. Further, as pointed out by 
Winslow (’98, p. 178) and Peter (’98) the otic process of the quadrate 
has disappeared, and there is certainly no bone which covers what 
may be considered as the external surface of the body of the quadrate, 
nor does one appear in later or in the adult stages. Hence it follows 
that, at least in Ichthyophis a true squamosal is lacking. 
There is, however, a membrane bone present (P/.) which develops 
over the postero-lateral edge of the parietal, the anterior dorsal part 
of the otic capsule, the adjacent dorsal portion of the trabecula, and 
