258 Part III— Twentieth Annual Beport 



bone is straight, whereas in the cod it is turned well up. The para- 

 sphenoid of the cod is readily separated from those of the saithe and lythe 

 by its greater thickness and strength. 



Prefrontal (pr. F.). 

 Cod, Fig. 46, PI. IX. : Saithe, Fig. ]0, PL IX. : Lythe, Fig. 25, PI. IX. 



Rising from the upper surface of the prefrontal there is a process to 

 which is attached a cartilage ligament, which is united in front to the 

 hind part of the ethmoid, and to a similar process on the prefrontal of the 

 opposite side. This process is very small in the lythe ; in the cod and 

 saithe it is large It forms part of the wall of the olfactory foramen, and 

 the anterior lateral part of the frontal rests upon it. 



In the cod the part of the bone which articulates with the base of the 

 ethmoid is very broad : in the saithe and lythe it is small. The anterior 

 part which articulates with the vomer is also bound to the large mass of 

 cartilage below the ethmoid. In the saithe and lythe the anterior inner 

 part of the bone which meets the same part of the prefrontal of the 

 opposite side is broadly curved to the base of the sutural process which 

 is inserted into the parasphenoid. It is shorter in the cod, being reduced 

 in size through the larger prefrontal-ethmoid sutural area. 



Postfrontal (pt. F.). 

 Cod, Fig. 44, PI. IX.: Saithe, Fig. 8, PL IX. : Lythe, Fig. 23, PL IX. 



The postfrontal articulates with the frontal in front, with the orbito- 

 sphenoid below, with the squamosal and prootic behind, and with the 

 parietal superiorly. The free part of its posterior side forms the anterior 

 edge of the articular socket which receives the head of the hyomandibular. 

 Part of the upper edge of the prootic shares in forming the lower edge of 

 the same, while the main articulating surface is on the squamosal. 



In the postfrontal one point of difference between the cod and the 

 other two species is in the shaj)e of the upper anterior angle, which lies 

 beneath the hind corner of the frontal at the notch in which is situated 

 the head of the fifth suborbital. In the cod the corner of the postfrontal 

 is triangular, whereas in the saithe and lythe it is rounded. 



In the cod the bone is united to the prootic by sutures in the whole of 

 the region in vvhich they are in contact, but in the saithe these two bones 

 are only united by a few sutures at the posterior end (and even these may 

 be absent), while the remaining portions of their edges are smooth, and 

 simply bound together by cartilage. In the lythe there is only an inter- 

 mediate portion free from sutures, both ends being serrated for 

 articulation. 



In the case of the orbitosphenoid, in all three species tlie outer layer of 

 the postfrontal lies over on the upper part of that bono without there 

 being any very close union. 



The part of the postfrontal which is seen in the top view of the skull is 

 small in the lythe, a little larger in the saithe, and largest in the cod. 



Sijuamosal (Sq.). 



Cod, Fig. 45, PL IX. : Saithe, Fig. 9, PL IX. : Lythb, Fig. 24, PL IX. 



The squamosal overlaps the postfrontal in front ; it articulates with 

 the prootic below, with the opisthotic below and behind, and on the 



