16 
continues forward across the external surface of the cartilage hy’ 
and reaches the internal surface of the palato-quadrate projection of 
the ventro-lateral edge of the skull. There a branch is sent forward 
to a mass of tissue that lies in a hollow on the internal surface of 
the palato-quadrate cartilage and that looks like degenerate fatty and 
muscular tissue, this little mass of tissue possibly representing the 
otherwise completely aborted pseudobranch. The anterior carotid then 
turns sharply dorso-postero-mesially and, having again crossed the 
external (anterior) surface of the cartilage hy‘, enters a long canal in 
the overlying cartilage, which canal, continuing in the direction of the 
artery, opens on the floor of the orbit. Having issued from this 
canal, the artery sends a branch outward with the nervus opticus to 
the eye-ball and then itself immediately perforates, posterior to the 
nervus opticus, the membrane that closes the large opticus perforation 
of the mesial wall of the orbit, and enters the cranial cavity. There 
it separates into anterior and posterior cerebralis arteries, the latter 
of which fuses posteriorly with its fellow of the opposite side to 
form a median myelonal artery. The branch that accompanies the 
nervus opticus and enters the eye-ball is called by ALuen the optic or 
retina artery, but this artery is certainly the homologue of the ophthalmica 
magna of ALLEN’s descriptions of the Loricati and not the homologue 
of the optic artery. In Chimaera monstrosa, the anterior carotid canal 
is said by Husrecur (l. c. p. 267) to perforate the basis cranii and 
open directly into the cranial cavity, which seems certainly to be an 
error. In Callorhynchus, the anterior carotid, as described by PARKER, 
is strictly similar to the artery in Chimaera colliei. 
The lateral dorsal aorta, anterior to the point where it receives 
the efferent first branchial arteries, becomes immediately a relatively 
small artery which ALLEN, in his figure and also in his drawings, 
has called the external carotid; but this artery, which is the posterior 
carotid of PARKER’S descriptions of Callorhynchus, is certainly the 
anterior prolongation of the lateral dorsal aorta and hence the homo- 
logue of the common carotid of ganoids and teleosts. Running at 
first anteriorly, this common carotid artery turns antero-mesially and 
then soon separates into its external and internal branches, the latter 
of which is not shown by Arten in this fish, nor by PARKER in 
Callorhynchus. 
The internal carotid is a small and delicate vessel, and running 
directly mesially, immediately beneath the ventral surface of the skull, 
