570 H. H. SWINNERTON. 



by ligament" (p. 41). The condition presented by the 

 Teleosts cannot, however, be completely described by any one 

 of these terms, for whilst it is true that the hinder end of the 

 palato-quadrate is suspended by a well-developed something", 

 which may yet be shown to have no homology with the 

 hyomandibular of Elasmobranchs, the fore-end is not merely 

 suspended by ligaments, but articulates directly with the 

 cranium, and may, as in Gasterosteus, Belone, and some 

 Siluroids, be continuous with the ethmoid cartilage until 

 a very advanced stage. This mode of suspension is therefore 

 hyostylic only posteriorly, but autostylic anteriorly. 



In the first stage in the development of Gasterosteus the 

 palatine process does not reach the end of the trabeculae. This 

 cannot be interpreted as an approximation to the Selachian 

 type, for the opposite processes are parallel. In early stages 

 of Acanthias the homologues of these processes have not met, 

 though the halves of the mandible are already united (Sewert- 

 zoff, 99, p. 289) . Similarly for other embryonic Elasmobranchs 

 and for the adult Notidanus (Gegenbaur, 72, p. 187). 



It has ah'eady been pointed out that a line of advancement 

 or retrogression can be recognised within the Teleostean 

 class, in the gradual reduction of the metapterygoid region 

 (Text-figs. 1 — 4). Reversing the order of procedure, and 

 passing from forms without metapterygoid process (fig. 1) to 

 those lowly forms in which it is strongly developed (fig*. 4), 

 other structures begin to appear. Thus, in the larval Amia 

 (PI. 31, fig. 60), the metapterygoid region, besides being 

 large and plate-like, sends from its upper border towards the 

 trabeculae {tr.) a large process (p.), the pedicle. Below the 

 exits of the optic and trigeminal nerves the trabeculae, which 

 are here pierced by the carotid artery (ca.), project slightly 

 towards it. 



In Salmo trutta (Text-fig. 4) the same condition prevails, 

 and the pedicle is almost equally well developed. This is 

 figured, but not referred to by Winslow (98). 



These facts suggest that at some former time an actual 

 connection or articulation must have existed between the 



