xx] 



SKULL 



477 



ethmoid region and so a better name for the skull would be amphi- 

 stylic. The upper half of the first visceral arch is ossified in front 

 by a palatine bone usually bearing teeth which articulates with 

 the parethmoid ; in its central portion by three bones, viz. an ecto- 

 pterygoid below and on the outer side, an entopterygoid on the 

 inner side, and a metapterygoid above; behind where it articu- 

 lates with the lower half of the arch (which forms the lower jaw) it 

 is ossified by the triangular quadrate bone. In the lower jaw 



A B 



-IS 



FIG. 234. A. dorsal and B. ventral view of the cranium of a Salmon, Salmo 

 salar, from which most of the membrane bones have been removed. After 

 Parker. Cartilage is dotted. 



1. Supra-occipital. 2. Epi-otic. 3. Pterotic. 4. Sphenotic. 5. Frontal. 

 6. Median ethmoid. 7. Parietal. 8. Lateral ethmoid. 9. Para- 

 sphenoid. 10. Vomer. 11. Exoccipital. 12. Opisthotic. 

 13. Alisphenoid. '14. Orbitosphenoid. 16. Foramen for passage 

 of an artery. 17. Pro-otic. 18. Articular surface for hyomandibular. 

 u, vn, ix, x. Foramina for the passage of cranial nerves. 



there is developed an articular bone which ossifies its hinder part 

 and articulates with the quadrate. 



The second visceral arch termed the hyoid is divided as in 

 Elasmobranchii into two regions an upper, which articulates with 

 the auditory capsule above and is firmly attached to the quadrate 

 region of the first visceral arch below, and a lower which swings 



