30 



head of the maxilla is brought into closer connection with 

 the posterior ascending process of the pre-maxilla. Then 

 again the posterior articular process for the maxilla at the 

 junction of the two arms of the pre-maxilla is smaller, and 

 instead of overlapping the maxilla is overlapped by it. 



Pre-Maiilla. — Both arms are longer and stouter. The 

 ascending arm is at right-angles to the oral arm instead 

 of at an obtuse angle as on the right side, and passes over 

 the inter-maxillary more to the middle line of that car- 

 tilage. It bore in this specimen 17 teeth as against 4 of 

 the other side, and set, as already stated, in a different 

 plane. 



The asymmetry of the suspensory and jaw apparatus, 

 whilst undoubtedly initiated by the torsion cf the 

 cranium, has also been independently emphasized by the 

 habits of the fish, as already described. The broad 

 anatomy of this distortion is as follows : (1) The suspen- 

 sory apparatus on the right side is mostly longer — thus 

 thrusting the jaws over to the left ; t (2) the motion of the 

 maxillse at the sides of the mesethmoid prominence and 

 over the head of the vomer and the course of the inter- 

 maxillary over the mesethmoid beak itself is an oblique 

 one with a set towards the left, which the pre-maxillse and 

 mouth must necessarily follow. The jaws themselves and 

 the bones immediately related to them are naturally more 

 robust on the left side, since their function is mostly per- 

 formed on that side. Hence the practical absence of teeth 

 on the right pre-maxilla and dentary. 



4. — The Opercular Bones (Fig. 5). 



Ocular Side. 



Operculum (O^j.). — A thin laminate bone containing 



no cartilage except at the articular cup. It is bifid pos- 



t Cp. Traquair, oj). cit., Tab. 30 and pp. 276-7. 



