362 



MANUAL OF ZOOLOGY 



is in some respects -extremely primitive. The spinal col- 

 umn is represented merely by a thick persistent notochord, 

 enclosed in a sheath, with, in the lampreys, small carti- 



oes.ct.d 



Fig. 222. — Head of Myxine glutinosa (A) and of Bdellostoma f orsteri (B) , from 

 beneath, br. ap, branchial aperture; br. cl. /, first branchial cleft; jnth, mouth; 

 tta. ap, nasal aperture; oes. ct. d, cesophageo-cutaneous duct. The smaller open- 

 ings in A are those of the mucous glands. (After W. K. Parker.) 



laginous processes representing neural and haemal arches. 

 The skull is cartilaginous, and is peculiarly modified. Be- 

 hind it in the lamprey is a remarkable basket-like apparatus, 



