Vv.rtvbrata. :}27 



i^-ujis ill tho i'artilii.!;x> ; Imt diiriiij^' i\w (l(>volt>pin(nit. uf sniiu' I'drnis, 

 tlio r!irt-ilHg(< is j)!irtiiilly w outircly iviiIucihI by Ixiiic. 'V\w liouo 

 lun't', as ill dthor n>x'i*'<i*<. oiHMifiicM \\w oxiu-t posilioii of the 

 otu'tilHji'o ; tliu luttcr is jjTtulually iibsorbcHl, bi>iu< ilcvcluiiiu^- siTniil- 

 tiuuH>iisly ill its phuH'. I'\)r tlio most part, luivviiviT, tlio bonus oF 

 tlu< skull (Icvolup ill tlio t'onu of pliitos, ui o in b r iv n o boiios, wliirli 

 uriso in tlio iioij;liboiiriiiji- tissiio, luul lio oxteriuil to the ctioiulvo- 

 onuiiuui, pai'tly (Hivoriii^- tlio K'4'** inoutioiiod ubiivo, partly oovoriiij;- 

 tlio oai-tila^'o itsolf. 'I'liis may porsist to a f^Toatoi- or loss oxtoiit 

 bolow (lio iiiouibraiu> boiuis (('.(/■, in many Toloosloi), or it may 

 oiitiroly (lisa|)(>oar. Tlio adult skull is, t-lioroToro, luado up partly (iT 

 binios, prot\)riiiod in oartilaj^'o (of wliioli a small amount roniains to 

 ooniHH't tlio soparato piooos),aiid [lartly id' inoinbraiio btnios (jciiiuHl 

 tog'otlior by oounootivo tissiio) ; tho so(iarato bonos aro ofton partly w 

 ontiroly fiisod in tlio adult, thi oitlun- sido of tlio skull aro attaoliod a 

 nuiubor of v i s o o r a 1 arohos (l''ij;'- !HM .1, p. -Uij.), wUicdi, liko the 

 skull, aro originally oartila^-imnis ; tlioy aro oiirvod bars lyini;' in tlio 

 wall of tlio nioutli; vontrally, tlio oorrospondin^- aiidios of tlio two sides 

 oithor uiiito dirootly (tUo tirst aroli) ; or tlioy aro oonuortod by a sorios 

 oF uiipairod oartilas^'inoiis or bimy pioi'os, or by a sinylo oiio (copithv 

 or basi-branoliials). 'I'lio tirst visooral aroli, tlio in a u d i b n I a r a r o li, 

 is stroiiii'or than tlio siiooooding- onos and is dividod into iippor and 

 lovvor portions, tlio p a I a t u-q u a d i-a t o and tlio mandibular 

 () I- Mookol's oartila^'o. Tho no\t, tho liyoiil, is nsuuUy alsii 

 woll dovolopod. Tlio rost aro tormod g' i U aro Los; in Fish and 

 Amphibia thoro aro usually four, tivo, or movo, thoug-h g-ouorally 

 at most, ouo (U' two. In most N'ortobruta tho visooral arohos, liko 

 v>tlior parts i.)f tho skoloton, booonio, in tho ooiirso of dov(>lopniout, 

 partially or oouiplotoly roplaood, or oovorod by bono; tho palato- 

 qiuadrato by tho palatino, ptoryi;\>id, and quadrato botios ; Mookol's 

 oartilaji'o. h\ ouo or luoro bonos, oto. Tho maxilla and proinaxilla 

 aro indopoudont of tho gill arohos ; tlioy aro pairotl bouos, pcosout 

 in most N'ortobrata, and fornilug- tho autorior boundary of tho mouth ; 

 tlioy dt'wlop in oounootivo tissuo, and havo no oartilaginous portions. 

 Tho foro-Unibs aro oonnootod with tho body b\ tlio sliouldor 

 tf i r d I . wliioli oonsists i,>n oithor sido of a oartilag'inous or bony arch, 

 sitnatod in tho autorior rog'iou of tho body : souu^tiuios tho two arohos 

 aro uuitod Ih'Iow, but usually thoy aro soparato. If ossitiod, oaoh aroh 

 may gvuorally bo soou to oonsist of a doi'sal s h o u Id o r- b 1 a d o 

 (soapula), abovo tho point of artioulatiou of tho limb, or i;-Unioid oavity, 

 and a voutral oi'raooid; in front i.>f tho lattor thoro is usually a 

 spooial bono, tho oollar-bono (olaviclo). Ooruooid and olaviolo 

 arv' usually attaohod antoriorly to tho storuuiu whou this is prosont. 

 Tho skoloton of tho foro-liiub itsolf is laminato iu I'isoos, oousistiug' 

 of radially arraugod oarCilag'mous or bony piooos. (For dotails 

 ,vvt' bolow uudor Piscos.) In all othor \'ortobrata tho skoloton of tlio 



