CHONDROCRANIUM OF SYNGNATHUS FUSCUS 449 



and larger than it is in the 8-mm. stage (fig. 11). The lamella 

 of the frontal ossification is continuous with the perichondrium 

 of the cartilage forming the dorsal margin of the foramen. Just 

 posterior to the foramen, the cartilage is more deeply giooved 

 for articulation with the hyomandibula than it is in the younger 

 stage. The articular surface does not reach as far posteriorly 

 as that part of the otic capsule containing the membranous 

 labyrinth (fig. 10). The membranous labyrinth has increased 

 greatly in size since the 8-mm. stage and consequently expanded 

 laterally, displacing to a more ventral position the cartilage which 

 formed the lateral wall of the otic capsule in the younger stage. 

 A thin lamella of cartilage surmounts the margin of the thicker 

 ventral portion and forms the dorsolateral wall of the capsule 

 in this region. The formation of the septa semicircularia has 

 not gone farther than in the younger stage and are as yet mem- 

 branous. The small fenestra basicapsularis present in the otic 

 capsule of the 8-mm. stage persists. Toward the posterior 

 portion of the cranium the mesiodorsal margins are continuous 

 with the cartilage of the taenia tectum medialis (fig. 11). The 

 latter is enclosed in an osseous lamella which represents the 

 beginning of the supra-occipital ossification. Some of the carti- 

 lage is in the process of resorption. 



The occipital processes which in the younger stages were 

 separate from each other have fused mesially, so that an occipital 

 arch is formed. The posterior margin of the arch projects for 

 a short distance beyond the sides of the arch. The fontanelle 

 left between the taenia tectum medialis and the occipital arch 

 is closed by membrane. 



B. The visceral arches 



The rostral cartilage has the same relation to the dorsal surface 

 of the ethmoid plate that it had in the younger stage, but the 

 premaxillary lamellae which are represented in the younger 

 stage by cellular masses have now ossified and extend laterally 

 from the rostral piece, overlapping the anterior ends of the 

 palatines. 



