640 
ME. W. K. PAEKEE ON THE STEUCTUEE AND 
Skull of Dactylethra. — Fifth Stage. The adult Toad*. 
The occipital condyles of Dactylethra are quite normal : they are principally seen on 
the upper surface (Plate 59. figs. 1, 2, 4, ocx.), and they look only a little outwards, 
much of the cartilage lying towards the articular mid line. The foramen magnum 
(fig. 4, f.m.) is very large and steeply placed ; it is squarish, the upper and lower margins 
being somewhat convex, and the lateral margin concave. A narrow tract of cartilage, 
above and below, separates the two great side bones, the exoccipitals ( e.o .) : these 
synchondroses are the super- and basioccipital regions (s.o., b.o.). The chondrosteous 
cranium is overlapped almost to the end by the fronto-parietal slab (f •]?.), and the basal 
region is only free at the very end from that long bony hulk, the parasphenoid ( pa.s .). 
A lobular process from each exoccipital mass arches over, on each side, the hind skull ; 
these lobes are united into one roof by the superoccipital synchondrosis. Below 
(fig. 2), the exoccipital bony mass is flat on each side of the handle of the long para- 
sphenoidal sword, behind. Then on each side where the handle narrows to the “ guard,” 
the sides of the skull-floor are largely scooped, which scooping is part of the huge 
Eustachian vaults ; for here the first postoral cleft forms a large chamber on each side, 
the door of these chambers being common *j*. 
Above, when the fronto-parietals have been removed (fig. 1), we see one large fonta- 
nelle ( fo .) reaching from the occipital ring to the front of the cranial cavity. There are 
no subsidiary fontanelles as in the comjnon kind (Plate 54. fig. 3). Nearly the whole of 
the side of this open roof is solid bone ; and this side wall, in the wider fore part, 
thickens and shelves over the cranial cavity, in some degree. Below (fig. 2) the bony 
substance has crept nearly up to the nasal domes ; and at the sides (fig. 3) to a short 
distance behind the “ palato-trabecular junction.” Nothing but cautious observation of 
many types and many stages will show what is the meaning of this abnormal girdle- 
bone, which is so unlike that of the Common Frog and Toad (Plate 54. figs. 3, 4 ; and 
“ Frog’s Skull,” plate ix.). 
Begionally, it corresponds with the whole sphenoidal territory of a Mammal (“ Pig’s 
Skull,” plate xxxv. figs. 4, 5), and its fore edge does but reach the hinder margin of the 
ethmoidal territory. To what a narrow, transverse headland of cartilage this once huge 
territory is reduced, may be seen by comparing this with the early stages ; here (figs. 1, 
2, 5, eth.) its breadth is not greater than that of the fore part of the fontanelle. The 
kind of ossification here seen is that which is common in Batrachia when the chondro- 
eranium becomes solid bone; the cartilage-cells first calcify, superficially, then true 
ostosis takes place in and among them, and, finally, the process reaches to the perichon- 
drium ; but there is no separate, preformed ectosteal lamina. 
* I have worked at the two skulls of the adult ; one kindly lent me by Professor Huxley, after partial 
dissection by him; and the other by Dr. Dobson, of Netley. Por Professor Huxley’s views as to the skull of 
Dactylethra, see his recent Article on the “Amphibia” in the Encyc. Brit. p. 755. 
t “ The Eustachian tubes [are] united into one pharyngeal orifice ” (Gray, “ On Dactylethra,” Proc. Zool. 
Soc., Nov. 8, 1864, p. 464). 
