SrUKCKdX-l ISIIK: 



1047 



plac'i' is (ir(.-ll|)i('il in the skull of tlic Tclcdsls (sec, I'dt 

 instiiiicT, the ri'.-iiiiinii of the l^cl. p. 1014, lig. 2HK, />', 

 par) l'\ til'' |i.-iricfals (/tarictid smlcs^ (in-. -jMli, par). 

 Their hind oxtrciuities arc parted l)V the said jirojcrt- 

 iiig iolu' ot the su]jraocci|)ital scute; they are sometimes 



sinallei' plates. All these variations may lie observed 

 in the same sprcics, e. i;-. in the <'ommMii Sturfjfeon. 

 The ineonstancN of form depends upon the eomparati\ol\ 

 lax eotuiexioii hetwecM these scutes and the skeleton, 

 the looseness incrcasinH' towards the snout, which is erene- 



contiguous throughout the rest of their length (tig. 286, ' rally covered with numerous, more irregular, smaller 



B), and in other cases their anterior ends are separated 



(tig. '2i>i\, A) 1)\' an osseous plate (I'f) fitting in ht'tween 



them tVoni in front. l)efore (hem and parth on the 



sides of their anterior extremities lie a pair of jjlates 



(frontiil sciitrs. fr). often hut slightly inferior to them 



plates, except on tlir sides, which are armoured in adult 

 specimens of the common Siurgeon \\ith large scutes in 

 a detinite row. (Mitside each parietal jilate lies a .«(/»«- 

 iiiosdl siiilc (In othei's called the fem])oral scute, sqii), 

 and in fi-ont of this, ahovc the orliit, on tlie outside of 



B 



Fig. 281). Upper siirfaci- of IIjp lieail in tlir S(nri;eon (Acijienser slurio). ' ^ of tlie niitiiral sizi-. Two fif;iiroB sliowiiij; \ ariations in llii- 



speciep; tiolli specimens taken a1 (.'hrislianslad. 

 d^, first dorsal send-; et. etliinoidal scute; etl. ectethmoidal scute; //■, frontal scute; mt. mastoid sciilc; n. anterior nostril; o. eye; ocs. occi- 

 pital scute; par. parietal scute; ptoli, postorbital scute; ptp, postteiiiporal scute; splio. sphenotic scute; spo, supraorbital scute; ,«;)?>, spiracle; 



squ. squamosal scute; tp, temporal scute; op, operculum. 



in si'ze. These correspond in situation to the frontal 

 hones of the Teleosteous skull, and are sometimes close- 

 ly applied to each other, but usually separated at least 

 in front (fig. 286, B), sotnetimes throughout their length 

 (fig. 286, A), either by an elongated ethmoidal scute (et), 

 which may even extend, as mentioned above, between 

 the anterior extremities of the parietal scutes, or by 

 several (up to .') or more and sometimes two-rowed) 



each frontal plate, a curved row of three .scutes, the 

 posterior representing a postfrontal bone {.sphenotic .sci(te. 

 splio), the anterior a prefrontal bone {ectethmoidal scute, 

 etl). and the middle one a supraorbital bone {sujyra- 

 orhital scute, spo). The lower end of the sphenotic scute 

 touches the top of an angular plate, the form of which 

 calls to mind the preopcrculum of the Teleosts, but 

 which here cf)m])oses the posterior and inferior limits 



i:ri-i 



