OF THE SKULL IN THE UEODELOUS AMPHIBIA. 
567 
The direction of the squamosal (sg.) shows that the angle formed by the suspensorium 
with the axis of the skull is more than a right angle ; this bone is now a very dense 
strong plate, knobbed and transversely ridged above and below, spiked in front, and 
lobate behind. 
The squamosal of the Amphibia represents the preopercular and the great “ supra- 
temporal” lying over and above it in Clarias capensis, both in one piece. But in 
Polypterus (Traquair, op. cit. plate 6. fig. 7, y ) we have the exact counterpart of the 
Amphibian squamosal. In the figure referred to there are four “ post-spiracular ” plates 
lettered z (p. 180); one of these appears on the right side only in Amblystoma (Plate 27. 
fig. 6, s.t.). I have seen this bone in no other of the group ; but it is as valuable a remnant 
as the spiracular cartilage of Menopoma , Spelerpes, and Desmognathus. 
The bone which Professor Huxley calls “ angulare ” now can claim the title I have 
all along given to it, namely, “ articulare ” (Plate 27. fig. 7, and Plate 25. fig. 7, ar.). 
It is not now even a deep trough, merely, for the articular part of the mandible, but 
has ensheathed the cartilage, converting much of it into bone, and rises high, and turns 
in considerably, in the coronoid region. 
The dentary ( d .) nearly reaches the angle ; it has much less affinity for cartilage than 
the articulare ; it is gently angular in the middle, and roundly inturned towards the 
mentum. The splenial ( sp .), with its fine saw-like row of teeth, is slender, and occupies 
most of the fore half of the inner face of the mandible. 
The two rami (Plate 25. fig. 6, d.ar.) together form half a long and elegant ellipse ; 
their apposed distal ends are enlarged, and tied strongly together by ligamentous 
substance. 
The shrinking and then the absorption of the gills has been attended with very 
curious changes of the other arches (compare Plate 25. figs. 5 & 6). 
The hyoid cornu (c.lvy.) was oval in section, therefore thick ; it is now a flat tape ; it 
is still attached to the mandible by the mandibulo-hyoid, and to the suspensorium by 
the hyo-suspensorial ligament ( m.h.l ., h.s.l.). 
The hypo-hyal ( li.hy .) was only a gently attenuating fore part of the main rod, just 
separated by a tract of fibrous tissue ; now it is a very slender terete rod turned back- 
wards from the cerato-hyal by a sharp angle, and it has coalesced with the front corner 
of the first basibranchial ( b.br . 1). 
The first epibranchial is still a stout cartilage, but the distal piece, or first cerato- 
branchial ( c.br . 1), has escaped from it, and thus the upper piece has travelled down to 
the basal piece. 
Moreover, the distal piece is now a mere hypo-branchial as to size, and, like the hypo- 
hyal, it has turned up, in the manner of a railway signal, becoming nearly parallel with 
the piece in front. 
The second cerato-branchial and both the next arches are absorbed, and the second 
epibranchial ( e.br . 2) articulates with the narrow end of the first basibranchial {lj.br. 1). 
That element is flatter in its front part, which is ossified, and longer in its hind part. 
