156 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



(fig. 4, Ep.P., Pa. P.), there is a marked difference from 

 the cod, the former being more prominent than ihe latter, 

 instead of vice versa. 



In a dorsal view (fig. 1) the asymmetry is most pro- 

 nounced in front of the parietal region. In the cod the 

 frontals completely meet (and indeed fuse) in the mid- 

 dorsal line. In the Plaice, on the other hand, there is a 

 very wide separation of the frontals anteriorly, so as to 

 form a large secondary frontal fontanelle or left orbit. 



The asymmetry is, however, more evident on the 

 ventral surface (fig. 2). This is due to the fact that in 

 front of the alisphenoids there is no side wall to the 

 cranium, which, therefore, here consists of the paras- 

 phenoid only. In front of the prootic the parasphenoid 

 turns sharply towards the eyeless side to such an extent 

 that the head of the vomer was, in the specimen figured, 

 deflected by about a centimetre from the middle line. As 

 the parasphenoid is the most prominent feature on the 

 base of the cranium, the appearance of torsion in this 

 region is, in a full-sized fish, most striking. 



Seen from the side the cranium on the eyeless side 

 falls more into one plane than on the ocular, but this is 

 obviously due to the inclination of the parasphenoid and 

 vomer to that side (cp. fig. 2). 



The interior of the brain case is extremely irregular. 

 Owing to the lateral walls meeting ventrally at a some- 

 what acute angle a false floor for the brain becomes neces- 

 sary, and this consists of two distinct parts. In front 

 there is a rather narrow transverse bridge connecting the 

 two alisphenoids, a strong sutural union being effected in 

 the middle line. Behind there is a similar but much 

 broader bridge joining the two prootics, the two processes 

 meeting as before in a median suture. The true floor of 

 the cranium is formed in the former of these cases by the 



