790 
ME. W. K. PAEKEE ON THE STEUCTUEE AND 
frontals (fig. 8) ; between the four bones, on the upper surface, is the well-known fonta- 
nelle (fig. 9, fo.). The posterior margin of the parietal has just reached the superocci- 
pital (s.o.). 
There is something very mammalian in the huge squamosals (Plate LXXXIV. figs. 
6-9, sq.) ; they are, however, perfectly ornithic, having little of the Batrachian character 
such as is seen in the Struthionidse ; they are twice as large, relatively, as in Birds gene- 
rally, and show a large square plate on the inside of the skull (fig. 7), thus supplementing 
the wall-plate of the prootic (pro.) and the alisphenoid (a.s.). 
The squamosals of the Fowl do not show the bifurcate character so well as in the other 
families of Birds and of several mammalian types — for instance, Cavia, Arvicola,Lepus, &c. 
It is here (fig. 8, sq.) that the squamosal overlaps the whole side of the skull, over the 
piers of both the mandibular and the hyoid arches ; thus, whilst it is the counterpart of the 
principal “ supratemporal ” of the Ganoid Fish, it extends over the region occupied by 
the “ pterotic : ” the posterior portion of the squamosal has a separate counterpart in 
the Lacertilia, just as in them the descending portion of the lacrymal is separately 
ossified. 
In the mandible, however, the splint bones are as numerous in the Bird as in the 
lizard; but the Fowl is exceptional in possessing no “coronoid” piece. 
The dentary (Plate LXXXIV. figs. 7 & 8, d.) runs backwards almost to the articular 
facet ; the splenial (fig. 7, sp.) is oblong, equidistant from the ends of the ramus, and 
hides half the Meckelian rod. 
The surangular (figs. 7 & 8, su.) is more external than internal ; the angular (a.) belongs 
equally to both faces, being laid on below ; it flanks the long posterior angular process 
of the endoskeletal ray. 
Sixth Stage. — Chickens about 3 Weeks old. 
At first sight there appeared to be but little alteration, except general advancement 
of the ossification, in this stage ; but the specimens examined were feebly grown, and 
had died in a somewhat atrophied condition. They yielded two new pairs of ossific 
centres— the postfrontals (p.f.) and the epiotics (ep.) — which I had never before succeeded 
in demonstrating in the Fowl ; these are shown in Plate LXXXIV. figs. 13 & 14. I am 
rather inclined to suppose that these bony patches were more distinct on account of the 
arrested growth of the chickens ; at any rate, they are very instructive, and the Fowl is 
thus seen to agree with the. Osseous Fish and with many families of its own Class in the 
separate formation of these bones. In my former Paper (p. 129) I stated that the post- 
frontal of the Bird is an ichthyic bone, the so-called postfrontal of the Lizard being a 
postorbital subcutaneous scale. In this, as in many other respects, it is not the Lizard 
but the Teleostean Fish which is the proper forerunner of the Bird. 
The epiotics (fig. 13, ep.) are small four-sided ectosteal plates, formed over the arch of 
the posterior canal, and having a somewhat indistinct and very transitory separateness 
from the exoccipital ( e.o .). 
