CROSSOPTERfGII. 



173 



entopterygoid, metapterygoid and quadrate ; the lower jaw has 

 an articular and mento-meckelian cartilage bone and an angular, 

 splenial and dentary, the two latter being dentigerous. On the 

 upper jaw 



1C. 'I A 



131 2 n 



: /\ , 10 



16 



15 



24 25 



19 



FIG. 99. Side view of skull of Polypterus with membrane bones 

 (after Traquair). 1 Nasal opening, 2 premaxUla, 3 ethmoid, 4 

 accessory nasal, 5 os terminale, 6 nasal, 7 anterior suborbital, 

 8 posterior suborbital, .9 postfrontal, 10 frontal, 11 prespira- 

 cular, 12 spiraoular bones, 13 parietal, 14 post-spiracular, 15 

 supratemporal, 16 post-temporal, 17 operculum, 18 sub-oper- 

 culum ; 19 preoperculum, 20 quadrate, 21 jugals, 22. articular, 

 23 angular, 24 dentary, 25 maxilla. 



are premax- 



illae, max- 

 illae and 



jugals (two). 



The hyo- 



m a n dibular 



is ossified 



and bent ; 



there is no 



symplectic. 



There is an 



ope rculum, 



s u b o p e r- 



culum and 



a large bone 



called preoperculum. There are also circumorbital bones and 



pre- and post-spiracular bones (Fig. 99), as well as two bones 



(12) the spiracular bones in the flap which covers up the 



spiracle. 



There are also three supra- temporals (15) and a post-temporal 



(16) on each side. The membrane bones are in the skin and their 



outer surfaces are smooth and tuberculated, and not exposed in 



uninjured speci- 

 mens. The pre- 

 maxillae and 

 maxillae bear 

 teeth, and the 

 vomers, ptery- 

 goid and para- 

 sphenoid are 

 covered with 

 fine closely set 

 teeth. 

 The cartilaginous shoulder girdle is small and contains a scapular 



and coracoid ossification ; it is overlaid by a series of clavicular 



bones, of which the supraclavicle is attached to the pos t- temporal; 



FIG. 100. Side view of palatoquadrate, hyoman dibular and 

 opercular bones of Polypterus (after Traquair). 1 vomer, 

 2 palatine (small and not appearing in palate), 3 ectoptery- 

 goid, 4 entopterygoid, 5 quadrate, 6 subopcrculum, Jf 

 operculum, 8 hyomandibular, 9 metapterygoid. 



