68 ILLINOIS BIOLOGICAL MONOGRAPHS {G& 



The number and size of these bones vary in the different famiUes of ganoids 

 and teleosts, but their position with regard to the eye and their relation to the 

 suborbital lateral line canal are constant. The older comparative anatomists 

 recognized them as the suborbitalia, or frequently as the infraorbitalia, setting 

 off the anterior bone of the series as the lacrimal on account of its size and 

 relation to the nasal capsule: Van Wijhe (1882) remarked in a foot-note, that 

 the developmental relation of these bones to the suborbital canal was a good 

 character for homologizing the bones in the different groups. The nomencla- 

 ture used in this paper is based upon that used by AUis (1898) in Amia. 

 McMurrich (1884b) found six bones in the series in Amiurus, but did not differ- 

 entiate nor make a detailed study of any of them. He says there are pores in 

 these bones for the passage of more or fewer mucous canal tubules. In reahty, 

 there are no pores for the passage of such tubules because these leave the 

 canals between the bones, issuing through the connective tissue in this region. 

 Collinge (1895) has given a partial description of the relations of the suborbital 

 lateral line canal to the infraorbital bones in Amiurus catus, and figures no 

 tubules between the lacrimal bone and the junction of this canal with the 

 supraorbital. Gegenbaur (1878) recognized seven elements in the infraorbital 

 chain of Alepocephalus rostratus, the posterior bones being situated in the 

 muscle fascia on the dorsal surface of the cheek muscles. A dermal tubule 

 passed to the exterior between each bone, and in the first of the series, which 

 is comparable to the main body of the lacrimal of Amiurus there were a num- 

 ber of tubules as in the same bone in Amia. 



Allis (1898) called the last bone of the infraorbital series in Amia, the post- 

 frontal, and justifies himself in so doing, by stating that the postfrontal never 

 fuses with the underlying postorbital perichondria! ossification and always 

 contains a part of the suborbital canal. He states that in some mem.bers of 

 the Characinidae, and Cj^Drinidae, and in Scomber, in which the dilitator 

 operculi muscle lies on the dorsal surface of the cranium, this postfrontal lies 

 above the muscle. The postfrontal of Amiurus fulfills all of these require- 

 ments and hence corresponds to the same bone in the groups mentioned. 



According to this view the infraorbital chain of bones is comparable to the 

 orbital ring of the Stegocephalans and Reptiles, in which there is usually a 

 large lacrimal anterior to the eye, a zygomatic below the eye, followed by a 

 postorbital, above which is a postfrontal. The fact that, although the zygo- 

 matic bone is a member of the maxillary series, it never bears teeth lends some 

 support to the assumption that it is a lateral line bone rather than dental in 

 origin. Most older authors homologized this ring of the fishes on purely 

 topographical relationships, to the jugal arch of the reptiles, and Bojanus 

 (1818) called them the ossa jugalia. Gaupp (1906) makes no statement con- 

 cerning this homology. Cuvier first applied the name postfrontal in the fishes 

 to that bone which is today recognized as the sphenotic, because he thought it 

 was the homologue of the postfrontal of the Reptiles. 



