134 



PISCES. 



and Salmon). The remains of cartilage are retained longest in tho 

 ethmoid region (Silurus, Cyprinua), while on the roof and base of the 

 skull all remains of cartilage are replaced, partly by membrane bones 

 and partly by the primarily ossifying occipitals (basi- and exoccipital) 

 and petrosals (periotic) as well as by the alisphenoids. 



The posterior part of the skull is connected with the vertebral 

 column without any special articulation (except in the Rays and 



Os 



Etkl 



Ethi 



Ssc 



FIG. 586. Cephalic skeleton of Perca Jluviatilis (regne animal). Os, snpraoccipital ; Oex, 

 epiotic ; Par, parietal ; Sq, squamosal (pterotic) ; fr, frontal ; Frp, poatfrontal 

 (sphenotic) ; PrO, prootic; Als, alisphenoid ; Ps, parasphenoid ; Ethi, median ethmoid; 

 Ethl, lateral ethmoid (prae-frontal); Hm, hyomandibular ; S, symplectic; Q, quadrate; 

 Mtp, metapterygoid ; Enp, endopterygoid ; Ekp, ectopterygoid ; Pal, palatine ; Vo, 

 vomer; Jm, intermaxillary (premaxillary) ; MX, maxillary; D, dentary; Ar, articulare ; 

 An, angulare ; Op, operculum ; POp, prae-operculum ; SOp, sub-operculum ; JOp, inter- 

 operculum ; Hy, hyoid arch ; Brx, branchiostegal rays ; Cl, clavicle ; Sc, scapula Cor, 

 coracoid ; Ssc, supraclavicle ; Ac, accessory bone. 



Chimsera), the os basilare having the conical depression and form of 

 a vertebral body. Between the exoccipitals (which contain the fora- 

 mina for the exit of the vagus and glosso-pharyngeal nerves) and the 

 supra -occipital, which is distinguished by a strong ridge, an epiotic 

 bone (occipitale externum) is inserted on either side (fig. 586, Oex). 

 Close to the epiotic bone is the opisthotic (Huxley), which varies 

 greatly in size and form (being very large in Gadus and small in 



