MOIU'HOLOGY OF TEI-EOSTEA.N HEAD SKEI,ETON. 588 



support the statemeuts (just quoted) of these authors very 

 strongly, but tells with equal strength against the relation- 

 ships of these forms to the Chastodonticlas and Ephippida?. 

 In Chsetodon plebeius (fig. 46), the ethmoid region is an 

 extremely specialised one of the Pagellus type, for though 

 the palatine lies against the parethmoid, it is united to that 

 exclusively by ligaments, and the articular surfaces have 

 aborted. The palatine, moreover, has the large maxillary 

 process so characteristic of the Acanthopterygii, and mobility 

 for the suspensory apparatus is gained, as in Cyprinoids, by 

 articulation between the palatine and pterygoid bones. 

 Judging by the character of the ethmoid region, and its 

 relation to the palatine alone, the relationships of the 

 Plectognathi, and the undoubtedly closely allied Zanclidse 

 and Acronuridaj, must not be sought within the Acantho- 

 pterygii ; nor, judging by the well-developed metapterj'goid, 

 and presence of both pterygoids, must they be sought in the 

 Scomberesocine series, but somewhere lower down. 



V. Summary and Conclusions. 



1. The cranial flexure, together with other features in the 

 shape of the embryonic head skeleton in Teleosts, is probably 

 a mechanical effect due to differences in the degree of 

 distensibility between the dorsal and ventral surfaces of the 

 brain, and to the presence of skeletal structures in close 

 association with the latter (pp. 507 — 509). 



2. The presence of an epiphysial bar, with consequent 

 division of the large dorsal, cranial foutanelle into an anterior 

 and a posterior portion, is a common feature among Teleosts 

 during development (pp. 516, 517). 



3. The Ostariophysi differ from all other Teleosts in the 

 retention of this early developmental condition of the cranial 

 roof in the adult (pp. 525, 526). 



4. The intra-cranial notochord, so far from undergoing re- 

 duction, Tiever at any stage ceases to grow (pp. 513, 516, 523). 



5. In Gasterosteus, during embryonic life^ those skeletal 



