432 



Comparative Morphology of Chordates 



Of living fishes, the only members of Holostei are the gar pike 

 (Lepidosteus) and the "mudfish" or "bow-fin" (Ami a). Both arc 

 North American fresh-water fishes (Fig. 333C, D). The vertebrae of 

 Lepidosteus are exceptional for fishes in being convex in front and con- 

 cave behind (opisthocoelous). The "alligator gar" may attain a length 

 of 10 feet. Amia is a comparatively small fish. 



Order Teleostei 



"Bony Fishes." Ossification of skeleton at the maximum for 



fishes (Figs. 334, 335). (The name "Teleostei," meaning "completely 

 bony," is not to be confused with "Teleostomi," referring to the 

 terminal mouth.) Tail-fin homocercal or diphycercal (Figs. 327, 

 334). Pelvic fins more or less reduced or sometimes lacking, and com- 

 monly placed more or less in front of their typical position at the rear 

 end of the trunk, in extreme cases (e.g., the cod and its allies, Gadidae) 

 lying actually anterior to the pectoral fins (Fig. 299). In some eels, both 

 pairs of fins absent. Scales usually simple, thin, overlapping plates of 

 bone developed in lower layer (dermis) of skin (Fig. 328) ; sometimes 

 elaborated into projecting spines (porcupine fishes) or other specialized 

 forms; sometimes lacking (eels, swordfish, many catfishes). Spiracles 

 always closed ; five pairs of gill-clefts or in some cases fewer. Intestine 

 has no spiral valve other than possible vestiges of it in a few cases. 



SUPRAOCCIPITALl 

 BASIOCCIPiTAl: 

 HYOMANDIBULAR> 

 SQUAMOSALS 



ST VERTEBRA 



NEURAL SPINE 



PAR I ETAL- 

 PARASPHENOID' 

 PTERYGOIDS>^ < ^ 

 FRONTAL"^<Wn§ 

 ECTETHMO ID-y25d£2^^^ 

 MESETHMOID 



NASAL— ,„ 



W///m 



MAX I LLA 



PREMAX I LLA 



ARTICULAR 

 DENTARY- 



\!SRANCHIOSTEGAL ^fe^i* 1 - 

 KAY1> ARCHES ( 



Fig. 335. Skull of hake in left lateral aspect. Membrane bones are cross- 

 hatched, cartilage bones stippled. Compared with the skulls of other fishes, that of 

 teleosts shows an increased dominance of membrane bones over those preformed in 

 cartilage. (Courtesy, Neal and Rand: " Chordate Anatomy," Philadelphia, The 

 Blakiston Company.) 



