r.r.i.-nsiiKs. 



1013 



fail tu sclcr.-il lidiics ill the \eiitrai luiif ol' the latcrMJ 

 iimsi-'ic. 'J'lirniiiiiiniit llic i^rcatcr ]iart of the ali(i(iiiiin;ii 

 ref,ni)ii, from tlie 8tii vertebra to the 44tli inclusive, we 

 find in the common l']el another pair of lower transverse 

 processes (parapophyses, y^/zyj), hehind the last-mentioned 

 processes and always smnllei' than these. On the 4')th 

 vertebra, oi- sometimes on the 4-lth, this posterioi' trans- 

 verse process on each side of the bone disappears, or 

 is at least, reduced more jjerceptibly than before; but 

 the anterior transverse ])rocess divides instead into two 

 (three) branches, the anterior (outer) supporting the 

 rib, the posterior (lia), which is simple or double, curv- 

 iiiiT inwards. <.)ii the 4(5th vertebra this posterior 

 i)ranch springing from one side of the vertebra joins 

 the corresponding l)r;incii of the other side, to form 



(an inner) ti'ansverse ])rocess, the former continued by 

 a row of transverse processes at the middle of the 

 sides of tin; caudal vertebra' (which row is wanting in 

 the common lud), the latter l)v the row which curves 

 downwards and inwards to form the hu'inal canal of 

 the caudal regicju. The skeleton of the Eel, for all its 

 simplicity, thus shows with the greatest distinctness how 

 the vertebral a|)pendages may be homologous in the 

 lower grades oi' differentiation, although, when i\u- 

 differentiation is more advanced, they are different 

 both in origin and functions. 



The ti|) of the tail presents the appearance of a 

 rather primitive (diphycercal) structure. Only the outer- 

 most (last) two vertebra' — the outermost of which is 

 coni])osed, at least in our common lud, of two pi-im- 



Fitr. 2C,7. Ski4i'lal parts cf tin- tip uf tl.c tail in Anijnilhi i-n!;/,in's, sciii fmiii tlie left side ami iiin.iriiififd. 



-l; from a yomi.e: Eel (Elver, Fr. Cn-rlle), aftor Robin; B: frcin n full-grown Eel. 



r, vertebra, originally the antepenultimate, subsequently tlie penultimate; yi, its ba>mal areh; h, its neural arch; m, its spinal eaual; ", urigi- 



iially penultimate verletira, afterwards confluent with the last vertebra; (', primordial articulation between these vertebrte; h, hindmost hiemal 



arches, surroundinsr the cavity of the lymph-heart; ^ termination of the spinal canal; ;•, lowest, .9, uppermost ray of the caudal tin; 



.1'. posterior expansion of the urostyle. 



the closed ha'mal arch and its h;ema] spine (pspi). In 

 the Conger the said posterior iiarapophvsis appears only 

 nil a few vertebra^ in the liindniost |)art of the ab- 

 dominal region, and even there is not always jjresent, 

 or is sometimes developed only on one side of the ver- 

 tebra-. But the parapophyses of the abdominal vertebra' 

 are broad, as in the Codfishes, and pierced at the base"; 

 ;ui(l ill file last H or 10 abdominal vertebrae the anterior 

 parapophysis divides info .in upper (outer) and a lower 



ordial vertebra; — enter into the structure of the a])pa- 

 ratus supporting the caudal fin. Although the vertical 

 tins of the Eels are, as a rule', so confluent that no 

 separate caudal tin can be distinguished extei-nally, the 

 presence of such a tin is indicated internally by the 

 circumstance that the hindmost tin-rays — 10, both in 

 our common Eel (tig. 267, r — s) and in the Conger' — 

 do not articulate like the others by means of a flat ar- 

 ticularv surface with separate intei'Spinal bones, but 



" In the JIurana the posterior parapophysis divides on the 2,5th vertebra, and from the 73rd vertebra inclusive its lower branch enters 

 into (he structure of tlie closed luenial arch: — see Owen, Anat. Phi/siol. Vertebr., vol, I, p. 45. 



'' In some, however, as in Oplnchthi/.^, the tip of the tail is free, without any trace of caudal tin. 

 ' In the MuRcna (i. 



