rmo 
o i 
DR. A. GUNTHER’S DESCRIPTION OF CERATODUS. 
strong, and forms, in front, a short and firm suture with its fellow, both hones diverging 
behind, the space between them being entirely filled by the anterior part of the basal 
bone (o). 
The central region is covered above by a median and two lateral flat thin bones, the 
latter being the continuations of the frontals: the former might be designated as sclero- 
yarietal (Plate XXXIV. a, and Plate XXXV. a). These bones are united with one 
another by squamous sutures, are more solid in front where they are connected with the 
ethmoid, and become thin and almost membranaceous near the occiput ; they form a 
continuous roof over the skull, but are separated from the cartilaginous capsule by the 
enormously developed and dilated musculus temporalis (see Plate XXXV. fig. 2, mt). 
This muscle is expanded as in a carnivorous mammal, and covers entirely the upper 
surface of the cartilaginous brain-capsule, taking its origin from the longitudinal median 
crest, and from some protuberances above the occiput. The lower side of this region 
is nearly entirely covered by the basal ( sphenoid ) bone (o). 
The lateral region has only one ossification ; it is a covering of the outer edge of the 
suspensory pedicle ; superiorly it is dilated into a lamina (Plate XXXIV. d, and Plate 
XXXV. d), which assists in forming the supramuscular roof of the skull. To the edge 
of the cartilage of this region is attached the g ill-cover apparatus, which consists of an 
operculum ( li ) and suboperculum (Plate XXXV. fig. 1, h!) ; a small cartilage behind, and 
hidden by the opercle, may be regarded as a rudimentary prceoperculum (Plate XXXIV. Jc). 
A further insight into the relations between the cartilaginous and osseous portions of 
the skull is obtained by a vertical section along its longitudinal axis (Plate XXXV. 
fig. 2. To this figure we shall have to refer subsequently, and in the explanation of 
the figures at the end of this memoir). 
Detailed Description of the Parts of the Skull. 
We proceed now to describe those details of the definable bones, cartilages, and other 
parts of the skull which are not included in the preceding general account. 
Distinct maxillary or intermaxillary elements are not developed ; they are replaced 
by facial cartilages, which can only be separated artificially from the external cutaneous 
integuments, and pass into the front part of the cartilaginous skull, and into the subor- 
bital ring. 
These superficial facial cartilages (Plate XXX. fig. 2, and Plate XXXIV. fig. 1) may 
be divided into three groups: — 1. The upper labial (/*'), surrounding the front part of 
the upper jaw, extending over the nasal region, and attached to the side of the ethmoid 
and, at the upper anterior angle of the orbit, to the frontal ; it is nearly continuous 
with (2) the infraorbital ring ( f ), in which three ossifications ( e ) are imbedded, viz. 
two on its origin behind the orbit, and one just below the eyeball. The infraorbital 
ring passes by a broad bridge into the lower lip. There is a large cavity (Plate XXX. 
fig. 2, c ) with several divisions in the interior of this bridge ; it is quite distinct from 
the labial cavity (p. 515), and appears to be entirely closed, without external openings ; but 
