302 THE ORIGIN OF VERTEBRATES 
the anterior portion of the velum is covered over with a scale-like 
or tubercular pattern remarkably like the surface-ornamentation 
Fic, 120.—AMMOC@TES CUT OPEN IN Mip-VENTRAL LINE TO sHOW POSITION OF 
VELUM; VELAR FOLDS REMOVED ON ONE SIDE. 
tr., trabecule ; vel., velum; B., anterior gnathic portion of velum; ps. b7., pseudo- 
branchial groove ; m,., muscles of lower lip segment; m,, muscles of thyro-hyoid 
segment; mé,, insertion of tubular muscles of velum near thyroid. 
seen in many of the members of the ancient group Eurypteride. In 
Fig. 121 I give a picture of this surface-marking of the velum. It 
is striking to see that just as in the case of the invertebrate this 
marking aud these serre are formed simply by the cuticular surface 
of the epithelial cells ; a surface which, according to Wolff, possibly 
contains chitin. The interpretation which I 
would give of the velar folds is therefore 
as follows :— 
They represent the fused basal parts of 
the opercular and metastomal appendages, 
, the gnatho-bases of the latter still retaining 
seh sig ie in a reduced degree their rasping surfaces, 
or Vutom. because, owing to their position on each side 
of the opening into the respiratory chamber 
they were still able to manipulate the food as it passed by them 
after the closure of the old mouth. 
The whole evidence points irresistibly to the conclusion that the 
mandibular or velar nerve of the trigeminal does supply a splanchnic 
