136 



ZOOLOGY 



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communicate directly with the 

 pharynx ; there is no respiratory 

 tube. 



The neural canal is over-arched 

 merely by fibrous tissue (Fig. 817, 

 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 

 cartilaginous plate. Similarly the 

 roof of the skull is entirely mem- 

 branous. 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 pro- 

 bably represents the first branchial 

 bar. The " tongue " is supported 

 by an immense cartilage (m. v.c.), 

 in part corresponding to the lin- 

 gual cartilage of the Lamprey. 

 The branchial basket is rudimen- 

 tary, being represented only by 

 certain small irregular cartilages, 

 such as one in the walls of the 

 cesophageo-cutaneous duct, and, 

 in Myxine (Fig. 817, br. &.), one 

 on the right side supporting the 

 common external gill-tube. 



The myotomes of one side 

 alternate with those of the other. 



The intestine is very wide. 

 The liver consists of two separate 

 portions, the ducts of which 

 open separately into the gall- 

 bladder. A pancreas-like gland 

 is present in both Myxine and 

 Bdellostoma. The brain differs 

 considerably from that of the 

 Lamprey, especially in the larger 

 olfactory lobes and the reduced 

 ventricles, and smaller mid-brain. 

 The dorsal and ventral roots of 



