of the Fishery Board for l^cotland. 255 



the saithe. In the lythe the flattened area is restricted mainly to the 

 part of the parasphenoid forming the floor of the cranium. Before it 

 reaches the level of the anterior border of the orbi to-sphenoid it is 

 replaced by a sharp ridge which splits anteriorly to receive the long 

 insertion of the vomer. 



The different shapes of the pra?frontals noted above are noticeable in the 

 view from below. Thus the outer oblique border of this bone in the 

 lythe and cod is turned a little more outwards than in the saithe. This 

 refers to the part in front of the pr?eorbital articular area, the anterior 

 edge of which is much higher in the lythe and cod, and so gives a greater 

 bend oiitwards to the edge in front of it. 



The cranium as seen from below is broader and more rounded in the 

 lythe and cod than in the saithe. 



Side View. 

 Cod, Fig. 38, PI. VII.: Saithe, Fig. 39, PI. VII. : Lythe, Fig. 40, PI. VII. 



In tliis view of the skull, the shape of its anterior extremity is seen to 

 vary with the three species. In the cod it is practically vertical to the 

 long axis. The front edge of the vomer lies exactly under the anterior 

 surface of the ethmoid, which articulates with the cartilage situated 

 between it and the adjacent parts of the premaxillaa. In the saithe the 

 front edge of the ethmoid slopes upwards and backwards at about an 

 angle of GO'* ; and while in the cod the angle between the upper and 

 front surfaces of this bone is practically a right angle, in the saithe this 

 angle is rounded off. In the lythe the front edge slopes backward a little 

 less than in the saithe. The main mass of the ethmoid is thrown 

 further back towards the frontals in the lythe and saithe than in the cod. 

 The anterior portion of the skull is more depressed in the former two than 

 in the latter. 



The interorbital space is more highly arched in the lythe than in the 

 saithe and cod. The posterior edge of this large space is formed by the 

 prootic and the ascending part of the parasphenoid which unites Avith 

 that bone. In the cod and lythe this portion of the parasphenoid is in 

 line with the lower edge of the notch of the prootic, whereas in the saithe 

 they meet in a fairly sharp angle. 



A very marked point of difference is seen in the side view of the 

 frontal-occipital spine. The frontal spine in the cod is low and runs very 

 gradually upwards into the occipital spine. In the saithe and lythe the 

 frontal spine is much higher and is convex in outline superiorly. Just 

 at a little behind the point where the frontal fuses with the occipital 

 spine there is an inbending in the upper edge of the spine. 



In three skulls of saithe, lythe, and cod of equal length, that is 

 measuring from the tip of the vomer to the hind edge of the basi- 

 occipital, the occipital spines extend backwards to about the same level. 

 The hind edge, however, in the saithe is longer than that of the lythe or 

 cod, since in the latter the supraoccipital and the hind portion of the 

 exoccipital come farther posteriorly than they do in the former. In the 

 lythe the exoccipital extends backwards to the level of the articular 

 surface of the basioccipital, while in the saithe it ends some distance in 

 front of it. In the cod there is an intermediate condition, the 

 exoccipital coming farther back than in the saithe and not quite so far as 

 in the lythe. 



In the cod and lytlie the squamosal bends downwards much posteriorly, 

 and to a distinctly greater degree than in the saithe. The high parietal 



