60 ILLINOIS BIOLOGICAL MONOGRAPHS [60 



rather than dermal. The olfactory nerve issues through this bone in the mail- 

 cheeked fishes, and in Amiurus, the olfactory tract. Both have a foramen for 

 the passage anteriorly of the ophthalmicus superficialis trigemini and a facet 

 for articulation with the palatine. 



The nasals. In the 32 mm. stage, the only ossifications in the roof of the 

 nasal fossa of each side were those developed around the anterior ends of the 

 supraorbital and suborbital lateral line canals. At that stage they were nar- 

 row and tubular, the more medial ossification enclosed the supraorbital and the 

 more lateral the suborbital canal. They were connected to the surrounding 

 bones by ligamentous tissue, there being no contact of ossifications. In the 

 adult, the more medial of the two bones is recognized as the nasal and the more 

 .ateral as the lacrimal. The nasal (Fig. 15) is flat and covers most of the fossa 

 roof, its concave antero-lateral margin forming the m.edian margin of the 

 anterior naris. The lateral line canal occupies a very limited space on the 

 longitudinal median dorsal surface of the bone. This canal opens anteriorly 

 by two pores, one at the tip of the bone (Fig. 11), and the other on the latero- 

 anterior margin, posterior to the anterior naris. Posteriorly, the lateral 

 line canal passes from the narrow posterior tip of the bone and proceeds 

 through a mass of connective tissue before entering the anterior end of the 

 frontal {fr.). The flat and scale-like appearance of the bone is the result of 

 ossification of part of the fibrous connective tissue below the lateral line canal 

 ossification. In outline the bone is suggestive of the nasal of Amia (Sagemehl, 

 1884), but it is not nearly as massive nor does it meet its fellow of the opposite 

 side. The enclosed lateral line canal does not connect with that of the other 

 side within the ethmoid as it does in Amia. The nasal of the Characinidae 

 (Sagemehl, 1885) is more like that of Amia, and comes in contact with the 

 ethmoid cartilage as in the latter, but not in Amiurus. The Cyprinoid nasal 

 is more nearly like that of Amiurus than of Amia or the Characinids. In 

 Salmo, (Schleip, 1903) the nasal develops in contact with the ethmoid cartilage 

 and encloses a lateral line canal. In Gasterosteus (Swinnerton, 1902), this 

 bone is very large and intimately comiected with the ethmoid cartilage; it 

 extends on to the ventral surface of the cranium after forming the roof of the 

 nasal fossa, but the presence of a lateral line canal within it is not mentioned. 

 In the Amphibia, R.eptilia, Aves, and Mammalia, the nasal bone occurs as 

 a dermal ossification on the roof of the nasal capsule. In some mamm.als the 

 cartilage of the capsule beneath this bone disappears, and a condition com- 

 parable to that of Amiurus results. The teleostean nasal bone is comparable, 

 then, in a certain degree with the nasal of the higher groups. In nearly all of 

 the teleosts however, this bone contains a lateral line canal ossification on its 

 dorsal surface. In Amiurus the bone is isolated, but in most of the other forms 

 it connects to a greater or less degree by suture with the surrounding bones. 



The lacrimals. A single lacrimal on each side of the head forms the lateral 

 roof of the nasal fossa (Fig. 15). Each is very small and narrow and contains 



