584 H. H. SWINNHHTON. 



elements immediately coucenied in the support of the jaws 

 and operculum, and in the attachment of associated muscles, 

 seem to undergo a considerable acceleration in the rate of 

 development as compared with the rest of the head skeleton 

 (pp. 534, 535). 



6. Among Teleosts and the immediately related Ganoids, 

 three types of palato-ethmoidal relationship exist (pp. 538, 

 539, 551—557). 



(ft) The Panartete, in which the palatine cartilage or its 

 derivatives is attached to the ventral surface of the 

 ethmoid for the whole length of this, from the par- 

 ethmoid to the pre-ethmoid cornua, e. g. Amia, probably 

 presented also by many Malacopterygii (Isospondyli). 



(b) The Disartete, in which the attachment is at the 

 parethmoid and pre-ethmoid cornua, but not at any 

 intermediate point, e. g. Esox, also presented by the 

 Salmonidas, Cyprinodontidas, Acanthopterygii, and prob- 

 ably some Malacopterygii (Isospondyli). 



(c) The Ac rartete, in which the attachment is confined 

 solely to the pre-ethmoid cornua, e. g. Gasterosteus, and 

 also presented by the Thoracostei, Scomberesoces, 

 Plectognathi, Zanclid^e, Acronuridte, and in a modified 

 form by Lepidosteus. 



7. The study of the adult anatomy and comparative 

 ontogeny of the head skeleton in Elasmobranchs and Teleo- 

 stomes seems to point to a common ancestral stock for these 

 two great divergent branches of fishes. It presented among 

 other features the following : 



A short embryonic life; weak cranial flexure; trabeculse 

 united to the extreme anterior end of the parachordals. 



A wholly cartilaginous cranium, possessing trabecular, 

 parachordal, and occipital portions (pp. 560 — 562). 



A cranium having a large dorsal fontanelle, which may or 

 may not have been divided by a transverse epiphysial 

 bar. Also two lateral fontauelles for the passage of the 

 optic, and possibly also the trigeminal and facial nerves. 

 Also a ventral or pituitary fontanelle. Also a large 



