146 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
The velar skeleton and the cartilaginous supports for 
the apex of the tongue are, for simplicity’s sake, omitted 
in all the figures. 
Hho ale 
Hig: 2. 
Tee, By 
Fig. 4. 
Kag. 5) 
Fig. 6. 
Outline sketch of the head of Petromyzon 
marinus, dissected to the level of the great car- 
tilages. The branchial cartilages, together with 
those which support the velum and lingual teeth, 
are omitted. Nat. size. 
Outline sketch of the corresponding parts of 
Bdellostoma Forstert. The antero-ventral cartil- 
age (a.v.) 1s represented as dissected to the level 
of the longitudinalis-lingue muscle, with its 
enclosed postero-ventral cartilage (p.v.), the for- 
ward course of which is represented by the dotted 
line a. 14 nat. size. 
Petromyzon marinus. ‘Transverse section to 
show the relationships of the median ventral 
cartilages to the lingual muscles. Taken across 
the line a f of fig. 1. Nat. size. ee by 
Bdellostoma Forstert. Corresponding section to 
fig. 3. Taken across the line « 8 of fey 2 
IS nat. size: 
The blackened areas in this and the preceding 
figure represent blood-lymph spaces. 
PLATE X. 
Dissection of cranium, with the labial and man- 
dibular-arch cartilages, of Callorhynchus antarc- 
ticus; male, serial with figs. land 2. Nat. size. 
The labial cartilages of Bdellostoma Forstert, 
enlarged, for comparison with those of Callor- 
hynchus. The specimen was exceptional, for the 
independence of~ the element lettered b.v. 
Twice nat. size. The lettering adopted in this 
