31] THE SKULL OF AMIURUS— KINDRED 31 



tween the posterior portions of this bone and the more medial nasal, the roof 

 of the nasal fossa is formed by the cartilage which supports the nasal barbel 

 (Fig. 22). This has no connexion with the chondrocranial cartilage and has 

 been named, the ' Nasenfliigelnknorpel, ' in the Characinidae by Sagemehl 

 (1885), who regarded it as the phylogenetic remnant of the nasal-flap cartilage 

 of the Selachians. 



The rudiment of the vomer (Figs.4, 22) appears as an unpaired dermal ossifi- 

 cation ventral tot he perichondrial ossification on the inferior surface of the 

 ethmoid cartilage. These two ossifications are distinct and have no connex- 

 ion as did the two types of ossification on the superior surface. There are no 

 teeth on the early vomer, which interdigitates posteriorly with the anterior 

 projections of the parasphenoid ossification by two pointed processes. This 

 interdigitation takes place below the posterior margin of the ethmoid 

 cartilage. 



The ethmoidal region of the developing Ganoids is, as far as is known, 

 entirely cartilage at a stage comparable to the 32 mm. stage of Amiurus. 

 The only place where perichondrial ossification has appeared is around the 

 ectethmoid process. The supraethmoid ossification is a distinctly dermal 

 bone, comparable to the dermo-supraethmoid of Amiurus, but has a transverse 

 lateral-sensory canal ossification on its dorsal surface connecting the supra- 

 orbital canals of the two sides. There is always a space, usually filled with 

 connective tissue, between this ossification in the Ganoids and the underlying 

 cartilage. The nasals of Amia are very much larger and flatter than the 

 corresponding bone in Amiurus and lie on the ethmoid cartilage. These bones 

 are developed in connexion with the latero-sensory canal system and enclose 

 the anterior ends of the supraorbital canals. The large nasals limit the supra- 

 ethmoid, so that it remains as a small triangular ossification at the anterior 

 tip of the cranium. The massive internasal septum of the adult Amia is 

 comparable to the same element of the 32 mm. Amiurus. The prefrontal 

 ossification (my ectethmoid) of Amia, is limited, even in the adult, to a small 

 area around the dorso-lateral margin of the ectethmoid process; whether or 

 not it develops perichondrially is not known. The vomer in Amia is paired 

 and toothed on its ventral surface, and is limited, as is the vomer of Amiurus, 

 to the medial part of the ventral surface of the cranium. As in Amiurus, the 

 palatine articular surface remains as cartilage. 



The ethmoidal region of the 32 mm. Amiurus, in its cartilaginous parts is 

 somewhat like that of a 25 mm. Sahno, as described by Gaupp. There is the 

 same massive cartilaginous internasal septum flanked by the nasal fossae, but 

 the anterior end of the ethmoid cartilage is rounded in Salmo and no ethmoid 

 cornua are present. The postero-dorsal extent of the ectethmoid process is 

 approximately the same in both cases, relative to the anterior end of the orbit, 

 but the foramen orbito-nasale is much higher in the cranial wall and farther 



