524 
DE. A. GUNTHER'S DESCRIPTION OE CERATODUS. 
Bisciioff’s opinion, that it is homologous with the jugal bone, does not appear to have 
been adopted by other anatomists. 
, The space between the two frontals, which in Lepido siren is filled by membrane, is 
ossified in Ceratodus (Plate XXXIV. fig. 1, a). Morphologically it is entirely distinct 
from the parietal of other fishes, corresponding to this bone in situation only. Its dis- 
tinctness from the parietal of Lepidosiren is evident, as this is a partial ossification of 
the skull-cartilage, and covered by the musculus temporalis, whilst it forms a case over 
this muscle in Ceratodus (Plate XXXV. fig. 2). It is evidently a conspicuous example 
of ossification of a fibrous membrane, and may be designated as sclero-parietal. It is a 
single bone, without median suture, subquadrangular, and of the same thickness as the 
adjoining part of the frontals; it passes behind into an occipital fascia, serving for the 
attachment of superficial muscles of the neck. 
To the description of the ptery go-palatine* bone given above, I have nothing to add 
(Plate XXXIV. I , and Plate XXXV, l). The two pieces which are found distinct in 
Fishes and lleptiles, and indicated by the compound name chosen by me for this bone, 
are here evidently merged into one; a bony arch extending from the tympanic suspen- 
sorium to the vomer necessarily includes both those pieces. Anteriorly the bones are 
united by a distinct suture (Plate XXXV. fig. 2, l'), which seems to disappear entirely 
in Lepidosiren. 
The tympanic pedicle (Plate XXXIV. fig. 3, s, and Plate XXXV. fig. 1, q), the sub- 
stance of which is cartilaginous, is strongly compressed in the direction from the front 
backwards ; it is strengthened on its inner surface by the apposition of the end of the os- 
seous pterygo-palatine, on the outer by a curiously shaped bone (Plate XXXIV. fig. 3, q, 
and Plate XXXV. fig. 1, q) which, as it is at least part of the os quadratum, may 
bear this name. This bone forms a not very thick covering of the outer edge of the 
tympanic pedicle. At its upper end it is dilated into a thin triangular lamella 
(Plate XXXIV. d , and Plate XXXV. fig. 1, d), the body of which is detached from 
the skull, entering into the supracranial roof formed by the frontals and sclero-parietal, 
and being of the same structure as those parts. Each suspensorium terminates in two 
condyles, the inner of which is rather narrower and much longer than the outer ; they 
are separated by a deep and rather wide groove ; these two condyles correspond to two 
articular surfaces of each ramus of the lower jaw. On the hinder side of the tympanic 
pedicle, near its base, there is a small round tubercle for the suspension and articulation 
of the hyoid arch j’ (Plate XXXIV. fig. 3, r). 
The body of the mandible (Plate XXXV.) is persistent cartilage ; but its entire outer 
and inner surfaces are covered by bone, forming an articular and a. dentary piece. 
In figure 1 the mandible is shown from the outer (articulary) side, in figure 2 from the 
inner (dentary). The relative position of the two osseous pieces is represented in 
figure 3. By making a vertical section across the middle of the mandible, as is repre- 
* In Lepidosiren paradoxa the “os palatinum ” of Biscbioff. 
t The agreement of the suspensory pedicle of our fish with that of the other Dipnoi is obvious. 
