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•TANK [. ROBERTSON. 
to efferent, or efferent to afferent sides of the arches. Tlie 
sliort-circniting channels of the sixth aortic arches do not 
expand so nmrkedly as do those of the fifth, fourth and third. 
Tlie sixth arches themselves dwindle in size, the fifth aortic 
arches now bringing the main supply of blood to the 
pulmonary vessels. The pulmonary vessels in turn, owing to 
the diminished calibre of the sixth aortic arches, finally have 
the appearance of arising directly from the dorsal aortic roots 
instead of from the arches themselves (Text-fig. 2, P.A.). 
The short-circuiting of the third aortic or first branchial 
ai'ches occurs somewhat differently and must be considered 
separately. About Stage 31 a new vascular channel appears 
at the junction of the third efferent aortic vessel with the 
dorsal aorta (Text-fig*. 23 b, L. A., x.), and passing dorsally to 
and obliquely across the afferent branch of the third aortic 
arch in the first branchial arch, reaches the root of the 
tongue, and is prolonged forwards along the side of that 
organ (Text-fig. 23 b, L. A.) as the lingual artery. Later 
this new vessel fuses with the third aortic arch just where 
that vessel passes into the first branchial arch at the root of 
the tongue (Text-fig. 23 b, xx.), that is to say, just at the 
outer termination of the lateral ventral aorta. The third 
aortic arch now disappears between this point of fusion (Text- 
fig. 23b, XX.), and the point of origin of the new artery from 
the dorsal aorta (Text-fig. 23 b, x.), so that the new vessel 
forms the short-circuiting channel for the third aortic arch 
(compare figs. 23 b and 23 c, L. A. xx. and x.). 
This apparent origin of the lingual artery from the dorsal 
aortic root must be regarded as a secondary condition due 
probably to the precocious development of the short-circuiting 
vessel of the third aortic arch. It is a temporary condition 
only, and with the formation of the short circuit a small vessel 
develops (Stage 38) at the junction of the lingual artery with 
the ventral aorta (Text-fig. 23 c, Hy. 1.), and passes outwards 
and backwards along a little gill-rudiment — hyoidean hemi- 
b ranch — that appears (Stage 38) in the angle between the 
first branchial arch and the lateral wall of the mouth. This 
