SKULL 



221 



the depression of the mesethmoid or hypophysial plate for the 

 support of the naso-pituitary canal, the forward prolongation and 

 median union of the palato- 

 quadrate cartilages of oppo- 

 site sides beneath the external 

 portion of the canal, appar- 

 ently for the support of the 

 latter,and the encircling of the 

 canal by supporting annular 

 rings of cartilage, (iv.) The 

 presence of two branchial 

 arches, connected, as in 

 Fishes, with a median basi- 

 branchial segment which 

 forms the middle one of the 

 three divisions of the lingual 

 apparatus, (v.) The reduction 

 of the complicated extra- 



FIG. 126. View of the upper surface FIG. 127. Dorsal view of the skull of Bdello- 



of the dental plate of Bdellostoma. stoma. Reference letters as in Fig. 125. 



t, Tendon of retractor muscle. (From (After Ayers and Jackson. ) 

 Ayers and Jackson.) 



branchial basket to small isolated cartilages in relation with the 

 gill-apertures and the cesophago-cutaneous duct, (vi.) The extra- 

 ordinary development of the lingual apparatus, of which it has 



