6 ON THE STRUCTURE OF TRACHYPTERUS ARCTICUS, 
epiotic—the latter slightly overlapping it; below with the epiotic; above with the 
frontal. It is prevented from entering into the formation of the inner surface of 
the skull-wall by the frontal, which sends a flat plate internal to it for articulation 
with the supra-occipital. Thus the parietals, overshadowed by the great size of the 
epiotics, and covered over by the post-temporals, form no longitudinal crest on the 
surface of the skull, as they do even in Regalecus. 
The frontals are very large bones. Each presents a large triangular outer 
surface which is subcutaneous, and rises posteriorly into a high crest to a level with 
the supra-occipital. The inferior surface of the bone, which makes a sharp supra- 
orbital ridge at its junction with the preceding, constitutes the roof of the orbit. 
The inner face forms in its upper portion the side-wall of the great groove in which 
slide the pre-maxillary processes, and in its lower portion is excavated to receive 
the great cartilage of the tegmen cranit which forms the floor of the said groove. 
The supra-orbital plate of the frontal articulates in succession with the mesethmoid, 
the orbitosphenoid, and the alisphenoid. The anterior narrow end of the bone 
articulates with the parethmoid.  Posteriorly the frontal articulates with the 
sphenotic, the pterotic, the parietal, the epiotic, and the supra-occipital. 
The nasals ave small, flat, thin, rectangular bones, and lie freely over the 
nostrils, attached by ligament to the frontals. 
The sub-orbital scutes are reduced to two in the anterior region on each side. 
The upper one, the lachrymal of Teleosteans, is much the larger. It is nearly 
rectangular in outline. Its outer surface is deeply erooved. Its inner surface is 
rounded. The lower one is flat, thin, and very small. The two bones are in 
eontact with one another ; both are sub-cutaneous. 
The basisphenoid is said by Parker to be entirely wanting in Regalecus, as 
also is the presphenoid. The latter bone is not to be found in Trachypterus, but 
the basisphenoid is well developed, though somewhat remarkably modified. This 
element, placed slightly anterior to the post-orbital pillars, rests below in a groove 
of the parasphenoid, and rises up as a sort of columella to join by its forked head 
the two prootics close to the alisphenoids, and immediately below a larger anterior 
cranial foramen. Anomalous as is the appearance of this bone, it is plainly the 
basisphenoid, displaced and elongated by the same causes which have led to the 
separation of the parasphenoid from its ordinary position in the base of the skull. 
The alisphenoids are thin, flat, squarish bones, articulating in front with the 
orbito-sphenoids, above with the frontals, behind with the prootics and sphenotics. 
Below they are in contact with one another in the ventral middle line anteriorly, 
and diverge posteriorly to bound the anterior portion of the anterior cranial foramen. 
Each orbito-sphenoid is also a thin, flat bone of similar appearance to the 
preceding. It also meets its neighbour in the middle line. It gives distinct 
evidence of a cartilaginous origin—the upper part of the bone being a wedge of 
cartilage encased in a thin shell of bone. It articulates behind with the alisphenoid, 
