MR. T. W. BRIDGE ON THE OSTEOLOGY OF POLYODON FOLIUM. 
705 
from the anterior margin of the suspensorium ; it is quite distinct from the palatine 
process, and in front of it there is a small free postpalatine segment which has been 
segmented off from the ethmo-palatine moiety in front of it. By stage C the post- 
palatine process has coalesced behind with the pterygoid bar, and in front is united 
by fibrous tissue to the remainder of the palatine outgrowth, almost precisely as in 
the Toad. 
This want of synchronism in the first appearance of the two outgrowths in the 
Axolotl is evidence sufficiently strong to effectually preclude the idea that the palatine 
cartilage is a segment cut off' from the pterygoid bar and united to the antorbital 
region of the trabecula. 
Having established the anatomical distinctness of the two structures in question 
both in the adult skull and in the embryo Axolotl, and, in addition, in the latter 
a sequence in the developmental origin of the two parts, we may notice briefly the 
condition of these parts in the Teleostei and in Elasmobranchs. 
In the Siluroidei there is a continuous bony outgrowth extending from the quadrate 
forwards to the prefrontal region. In no specimen of this family which I have had 
the opportunity of examining have I been able to detect any segmentation in this 
osseous bar, which either ends freely in front, or is attached by fibrous tissue to the 
vomer or to the prefrontal. A shaft-like cartilage-tipped bone is attached anteriorly 
to the prefrontal, and behind overlaps the outer or inner side of the previously 
mentioned osseous bar. 
The latter clearly corresponds to the pterygoid process of the Amphibia, while the 
shaft-like bone is in every way comparable to the retral palatine process of the 
Axolotl and the Toad. In some Siluroids there is a facet on the middle of the inner 
face of the palatine bone by which it is applied to the prefrontal bone ; this facet 
represents the ethmo-palatine process of the Toad, and the shaft-like bone thus 
exhibits prepalatine and postpalatine regions. 
In the common Eel the primitive pterygoid cartilage is not wholly converted into 
bone, and a short slender piece of cartilage is left creeping along the inner side of the 
unsegmented osseous pterygoid. The palatine process is apparently absent in the 
adult. In the Conger Eel, however, the palatine process is a large unossified mass 
of cartilage applied to the outer side of the anterior end of the bony pterygoid process, 
and closely united by fibrous tissue to the persistently cartilaginous ethmo-trabecular 
region. The attached face of the palatine is slightly grooved, and between it and 
the ethmo-trabecular cartilage the rostral branch of the second division of the fifth 
nerve passes, precisely as is the case in the Skate. 
From the Siluroid to the ordinary Osseous Fish the step is a short one, and if 
transitional links are needed they may be found in the Cyprinoidei and other gene- 
ralised physostome Teleostei. In the Carp the ossified palatine process is attached by 
ligament only to the pterygoid process, and forms in conjunction with the latter a 
palato-pterygoid arcade. The regional distinctness of the palatine is well marked ; 
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