140 



Z00L(3GY 



SECT. 



I. 1 



•« 



^t\ 





^ 



r,'^- 



o C S 

 S <a a 





s 



3 ;s o 



S ^'~ 





'^ 3 - _• 



£5 1> i P 



^ » o 

 .*^ "d J3 !ji 



P ^ . ^-' 



^ O ■' T. 



gs? s 



W r- !« u 



O 3 2 p 

 S .£•? 



<D ^' "^ X 



M * » ^- 



""* ^ ■4-> T 



be—'? 



"Hi" 



■*^ ' ^L. 



5 ^ S « 

 M .* -! 



CC _2 . ^ "^ 



1 -U^^ 



t 



o 2 t- u 

 00 g ce - 



the gill-pouches, which is again 

 connected with the pharnyx bj^ 

 another tube. Behind and close 

 to the last gill-slit, on the left 

 side, is an aperture leading into 

 a tube, the cesophageo-cntancmts 

 dud {ois. ct. d.), which opens 

 directly into the pharynx. In 

 Myxine (Fig. 807) the tubes 

 leading outwards from the gill- 

 pouches all unite together before 

 opening on the exterior, so that 

 there is only a single external 

 branchial aperture (hr. cvp.) on 

 each side ; into the left common 

 tube (c. Ir. t.) the oesophageo- 

 cutaneous duct {ors. ct. d.) opens. 

 In both genera the internal 

 branchial apertures communicate 

 directly with the pharynx ; there 

 is no respiratory tube. 



The neural canal is over-arched 

 merel}^ by fibrous tissue (Fig. <S07, 

 n.t.) ; there is no trace of neural 

 arches in the trunk, but in the 

 posterior part of the caudal region 

 both neural canal and notochorcl 

 are enclosed in a continuous car- 

 tilaginous plate. Similarly the 

 roof of the skull is entirely 

 membranous. The nasal passage 

 {net. t.) is strengthened by rings of 

 cartilage, and the buccal tentacles 

 are supported by rods of the 

 same tissue. Behind the styloid 

 cartilage or hyoid bar (sf.j).) is 

 a rod connected below with the 

 sabocular arch ; it probably re- 

 presents the first branchial bar. 

 The " tongue " is supported by 

 an immense cartilage (m. v. c), 

 corresponding to the lingual 

 cartilage of the Lamprey. The 

 branchial basket is quite rudi- 

 mentary, being represented only 

 by certain small irregular car- 

 tilages, such as one in the walls 



