MR, T. W. BRIDGE ON THE OSTEOLOGY OF POLYODON FOLIUM. 
685 
at their extremities both in front and behind, and are connected on each side with short 
transverse processes from the inner edges of the lateral splints, c 1 and c~. Anteriorly, 
they are sutnrally united to a second pair of splints of much the same character (lr), 
which, however, are not in contact along the median line, but are separated by the 
interposition of the median azygous element, a 1 . The lateral splints, c l and c 2 , are 
applied along the lateral margins of the chondrocranium. The former is somewhat 
Y-shaped, with one arm much shorter than the other. The stem is produced back- 
wards to the level of the pointed process formed by the bones b 1 , to the expanded 
hinder ends of which the short arm of c 1 is attached, while the long arm passes for- 
wards and unites with c 2 . From the inferior surface of c 1 a vertical lamina of bone 
descends, and is applied by its oblique anterior margin along the whole length of 
a diagonal ridge that traverses the lateral aspect of the cranio-spinal cartilage and 
to the decurrent flap of cartilage in which the ridge terminates behind and above. 
Posteriorly, each vertical plate diverges outwards and becomes separated from the 
cartilage of the coalesced anterior vertebrae by a mass of muscle. The next lateral 
splint, c 2 , continuously overlies the pterotic ridge and sphenotic process, roofs in the 
orbit, and extends forwards to the nasal capsule. A process from its inner margin 
unites it with the junction of the bones, b l and lr. An elongated oval fontanelle, 
covered in by membrane in the fresh skull, is left on each side, between the splints 
b l internally, and c 1 and c 2 externally, and through its anterior part the cranial carti- 
lage and the parietal foramina can be seen. 
A much smaller median fontanelle also exists between the splint a 1 and the hinder 
extremities of the splints b 2 , and a second pair of oblong lateral fontanelles are limited 
internally and externally by the bones b 2 , c 2 , and c 3 . Looking into either of the last- 
mentioned vacuities, the cranial cartilage and the orbital cavity can be seen. Con- 
tinuing forwards the series c 1 and c 2 , there is a third splint, c 3 , which extends from the 
roof of the nasal sac along the lateral margin of the base of the rostrum as far as the 
anterior ends of the median bone a 1 and the paired lateral splints b 2 . We have, 
therefore, at the base of the rostrum three longitudinally arranged series of splints, 
viz. : a 1 , b l and lr, and c 1 , c 2 , and c 3 , forming a medio-dorsal, an inner lateral, and an 
external lateral series ; and from this point the bones of each series are serially 
repeated along the roof of the rostrum to its anterior end, but instead of being inter- 
rupted by fontanelles, the rostral roofing splints are firmly adherent to one another 
by their thin overlapping squamose margins. There are three successive median 
splints, a 2 , o:\ and a 4 , which are disposed along the medio-dorsal line of the rostrum. 
The series b is continued along the rostrum by the paired splints, b'\ b h , and b 5 . It 
will be noticed that the paired bones of this series are in contact along the median 
line, and alternate with the azygous elements of the series a. The bone c 3 is in like 
manner repeated by one or two long splints applied to the supero-lateral margin of the 
rostral cartilage ; but as these are much overlapped by the rayed marginal ossicles cl 1 , 
they are not visible until the latter have been removed, 
