65] THE SKULL OF AM I URUS— KINDRED 65 



any of these lower teleosts and it would be interesting to find out how much car- 

 tilage remains beneath them. 



In the Cyprinidae (Sagemehl, 1891), the frontals have relations which closely 

 approach those of Amiurus, but the anterior fontanelle is always closed in 

 those genera figured by Sagemehl. The epiphysial bar persists as cartilage in 

 the adult, and the frontals have not extended beneath it as they have in Amiur- 

 us. In none of the forms thus far mentioned have I been able to find a frontal 

 ridge for the adductor mandibularis muscle comparable to that in Amiurus. 

 The postfrontal (sphenotic, auct.) never has the dorsal extent that it has in 

 Amiurus, but is always overlapped by the posterior margin of the frontal. 



- In the Salmonidae, the frontals lie superficial to the tegmen cranii (Parker, 

 1872), as they do in Esox (Huxley, 1864) and take very little part in the forma- 

 tion of the orbital roof, probably because of the persistence of the cartilage in 

 this region. Further discussion of the topographical relations of the frontals 

 is unnecessary because the above shows that there is a general agreement in 

 position throughout the whole group of teleosts. 



The relations of the nerves to this bone were neglected by the older anato- 

 mists and not until Sagemehl's description of Amia were these studied. As in 

 Amiurus twigs from the ophthalmicus superficialis facialis (Sagemehl's fifth) 

 pass into the bone to innervate the sense organs of the lateral line canal. The 

 Selachians have a series of foramina in this same region penetrating the supra- 

 orbital cartilage (Gegenbaur, 1872; Wells, 1917). In the Characinidae the 

 ophthalmic branch of the facialis has the same relations as in Amia and Amiu- 

 rus. In Amia an anterior branch of it extends dorsally through the cartilage 

 and frontal at the anterior end of the orbit. In the Characinidae, Cyprinidae 

 and Amiurus, this branch passes to the dorsal surface of the cranium through 

 the frontal alone. In Amiurus it lies free in the orbit in the younger stages and 

 its enclosure within the frontal is accomplished by growth ventrally from the 

 frontal of osseous spicules which finally enclose the nerve within a canal. 



Von KoUiker (1850) was one of the first to work out the histological develop- 

 ment of the frontals. Up to his time there was a controversy between those 

 who thought that the bone was developed from membrane and therefore com- 

 parable throughout the whole vertebrate series, and those who held that in the 

 Aves and Mammalia it was developed from cartilage. Reichert (1849) was 

 responsible for the latter statement and von KoUiker took it upon himself to 

 settle the controversy by histological and chemical analysis. The chemical 

 analysis of the bone showed that it did not have a trace of the chondrin common 

 to the bones developed from cartilage. As a result of his work he came to the 

 conclusion that the frontal bone throughout all the groups was developed from 

 dermal connective tissue and had nothing to do in development with the under- 

 lying cartilage. Subsequent researches on the development of the bone have 

 borne out his statement. Gegenbaur (1864) and Hertwig (1876) both agree 

 that originally the frontal bones were dermal scales which, in the course of 



