13 
ALLEN, in his figure, and in his drawings also, shows the dor- 
sal commissures that connect the anterior and posterior arteries in 
each of the first three branchial arches, but he does not show the other 
commissures above described, and the dorsal commissures shown by 
him lie external to the related afferent arteries instead of internal to 
those arteries, as I find them. In Callorhynchus, no posterior efferent 
arteries are shown by Parker in the branchial arches, and that author 
furthermore says (I. c. p. 689): “In Holocephali and Teleostei there is 
only one efferent artery to each gill, corresponding to the anterior of 
the two efferent arteries in the plagiostome holobranch. This is 
very evident in Callorhynchus, in which the single efferent artery 
of each gill is always cephalad of the corresponding afferent trunk.” 
From the efferent loop around the ventral end of the first gill 
cleft a commissural vessel has its origin, and passing dorsal to the 
truncus arteriosus runs into and is continuous with its fellow of the 
opposite side. From the anterior edge of this efferent loop, on either 
side, two arteries have their origin, in my specimen, these two 
arteries being shown as branches of a single artery in ALLEN’s draw- 
ings. Both branches run forward dorsal (internal) to the afferent 
hyoidean artery and ventral to the distal end of the ceratohyal, one 
going to the hyoideus inferior muscle of Vrrrer’s (1878) descriptions 
and the other running forward along the internal surface of the 
mandible near its ventral edge. The basal portion, at least, of this 
latter branch must accordingly represent that anterior prolongation 
of the internal lateral hypobranchial that, in elasmobranchs, becomes 
the persisting ventral portion of the afferent mandibular artery. 
From the loop around the ventral end of the third gill cleft, on the 
right hand side of the body but not on the left, in each of the three 
specimens examined, an artery has its origin and first sends a branch 
ventral to the truncus arteriosus to the coraco-branchialis muscle of 
the opposite side, and then a branch to the same muscle of its own 
side. The artery then runs backward external (ventral) to the third 
and fourth afferent branchial arteries, in the position of an external 
lateral hypobranchial, and soon separates into two parts. One of these 
two parts is the hypobranchial of its own side, which artery, running 
postero-dorsally, sends branches to muscles and tissues of the region 
and then falls into the subclavian artery. The other part of the 
external lateral hypobranchial soon becomes a very delicate vessel 
which passes ventral to the truncus arteriosus and there anastomoses 
