448 MH. C. TATE UEGAk ON trig 



Behind the orbital region the parasphenoid expands, the 

 anterior edge of each wing forming a transverse condyle for 

 articulation with the metapterygoid. Parke»'s researches show 

 that these condyles originate as separate ossifications in cartilage, 

 and he terms them alisphenoids, but in the adult fish they are 

 completely ankylosed with the parasphenoid. 



The true alisphenoids were not seen by Parker ; they are well 

 developed and separate : they meet the pro-otics behind and are 

 in contact with the f rentals above ; anteriorly they join the 

 orbitosphenoids, which converge and ankylose anteinorly to form 

 a short vertical plate that rests on the parasphenoid : just behind 

 this anterior plate the orbitosphenoid is pierced on each side for 

 the passage of the olfactory nerves (text-fig. 4). 



The parasphenoid condjdes are continued on to the pro-otics, 

 which intervene between the parasphenoid and the sphenotics ; 

 inner laminsB of the pro-otics meet in the middle line and form a 

 roof for the myodome ; the pterotics ossify downwards a short 



Text-fio-ure 3. 



Lepidosteus 'platystomus. Diagrammatic transverse sections of tlie snout : A, at 

 the level of the posterior end of the maxillar}' ; B, at the middle of the length 

 of the prsemaxillaries. ' 



c. rostral cartilage; f. frontal; n. olfactory nerve; p, parasphenoid; 

 pm. prsetnaxillary ; v. vomer. 



distance in the cartilaginous wall of the otic region, and the 

 epiotics are well developed ; there are no opisthotics. The ex- 

 occipitals meet, and behind them upper wings of the basioccipital 

 almost'meet in the middle line, roofing the foramen magmim. 



Gircicmorhitals, etc. (text-fig. 5, A). — The orbit is surrounded 

 by a complete series of 12 circumorbital bones ; these appear 

 externally as flat plates, but internally they are strengthened by 

 a stout circular ridge. Thex^e are 3 prteorbitals, the anterior 

 overlapping the end of the maxillary. Behind the circumorbitals 

 the cheek is covered with a number of irregularly ari-anged 

 plates. 



Jaws, Suspensoriura, etc. (text-fig. 5). — The prsemaxillai-ies have 

 already been described. The maxillary is segmented into 8, 

 the anterior piece fii-mly fastened to the side ©f the prsemaxillary, 

 the others attached to the palatine and ectopterygoid. 



In the lower jaw the concave surface for the articulation of the 

 convex condyle of the quadrate is formed by the posterior face of 



