140 



ZOOLOGY 



SECT. 



the gill-pouches, which is again 

 connected with the pharnyx by 

 another tube. Behind and close 

 to the last gill-slit, on the left 

 side, is an aperture leading into 

 a tube, the asophageo-cutanemtiS 

 duct (ces. 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 (br. ap.) on 

 each side ; into the left common 

 tube (c. br. 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. 807, 

 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 notochord 

 are enclosed in a continuous car- 

 tilaginous plate. Similarly the 

 roof of the skull is entirely 

 membranous. The nasal passage 

 {na. 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 {st.p) is 

 a rod connected below with the 

 subocular arch ; it probably re- 

 presents the first branchial bar. 

 The "tongue" is supported by 

 an immense cartilage (m. v. e), 

 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 



