512 



separating, somewhat dorsal to the middle point of its arch, into two 

 branches. These two branches of the first afferent branchial artery 

 continue upward in their arch and when they reach the dorsal edges 

 of the related clefts the anterior branch turns forward dorsal to the 

 anterior cleft and unites with the dorsal end of the afferent hyoidean 

 artery, the posterior branch turning backward above the posterior cleft 

 and uniting with the dorsal end of the anterior branch of the second 

 afferent branchial artery. In the second, third and fourth branchial 

 arches exactly similar conditions are found, a series of loops thus 



Fig. ] . Psendobranehial, carotid and branchial arteries in Chlamydoselachus ; the 

 dorsal aorta being swung upward and the truneus artei-iosus downward so as to bring 

 the vessels all into the same plane. 



Index letters. 

 aa I. II etc. afferent arteries in the 1st, 2nd etc. branchial arches, a.cer aaterior 

 cerebral artery. ahy afferent hyoidean artery. amd afferent mandibular artery. 

 apsh afferent pseudobranchial artery. cc common carotid, ch choroid, da dorsal 

 aorta, ea I. II etc. efferent arteries in the 1st, 2nd etc. branchial artei'ies. ec ex- 

 ternal carotid, ehy efferent hyoidean artery, epsb efferent pseudobranchial artery. 

 ic internal carotid. Ida lateral dorsal aorta, om arteria opbthalmica magna, op optic 

 artery, p. cer posterior cerebral artery, psb pseudobranch. ta truneus arteriosus. 



being formed above each gill cleft, excepting only the sixth; these 

 loops, which apparently contain a continuous lumen, connecting each 

 afferent artery with the next preceding and next following ones. Ex- 

 actly similar loops are formed around the ventral end of each gill 

 cleft by the end to end anastomosis of recurrent branches from each 

 of the adjoining afferent arteries. In the fifth branchial arch the 

 afferent artery is single throughout its entire length, but a recurrent 

 branch of the artery partly encircles the ventral end of the sixth gill 

 cleft. In the hyoidean arch the afferent artery is also single, but a 



