476 TELEOSTEI [CH. 



a basi-occipital which ends in a concavity resembling the end of 

 one of the centra. The base of the interorbital septum is gripped 

 by a Y-shaped bone called the basisphenoid and above it in the 

 septum are developed alisphenoids behind and sometimes but 

 not always orbitospherioids in front. 



The ethmoid region is ossified by a median mesethmoid bone 

 in the mid-dorsal line by two lateral parethmoids one at each side. 



No part of the cartilaginous nasal capsule is replaced by bone, 

 but the auditory capsule is ossified by no less than five bones, whilst 

 its inner wall which separates it from the cranial cavity is reduced 

 to membrane. The bones which ossify its outer wall are (1) a 

 pro- otic in front and below, (2) a sphenoticin front and above 

 spreading into and partly ossifying the interorbital septum as well, 



II 



FIG. 233. Lateral view of the cartilaginous cranium of a Salmon, Salmo salar. 

 After Parker. A few membrane bones are also shown. Cartilage is dotted. 



1. Supra-occipital. 2. Epi-otic. 3. Pterotic. 4. Opisthotic. 



5. Exoccipital. 6. Basi-occipital. 7. Parasphenoid. 8. Sphenotic. 

 9. Alisphenoid. 10. Orbitosphenoid. 11. Ectethmoid. 



12. Olfactory pit ; the vomerine teeth are seen just below. 14. Pro-otic. 

 15. Basisphenoid. 16. Foramen for the passage of an artery. 17. An- 

 terior fontanelle. 18. Posterior fontanelle. i, n. v, vii, ix, x. 

 Foramina for the passage of cranial nerves. 



(3) an epi-otic above on the upper surface qf the capsule usually 

 produced in a pyramidal projection, (4) a pterotic running hori- 

 zontally along the outer surface, and affording an articular surface 

 for the second visceral arch, and finally (5) an opisthotic forming 

 the hinder wall of the capsule (Figs. 233, 234). 



The skull of the Teleostean fish is usually described as hyostylic 

 because the upper part of the second visceral arch is developed into 

 a hyomandibular element in order to support the hinder part of the 

 first visceral arch as in most Elasmobranchii, but the front part of 

 the first visceral arch has a direct articulation with the skull in the 



