691 
BLOOD-VESSELS OF MUSTELUS ANTARCTICA. 
imbedded in the perichondria] lining of the cranial cavity, it sends off a branch (w) 
which passes inwards and backwards, crossing its fellow of the opposite side in the 
thickened perichondrium of the pituitary space, and finally anastomosing with the 
posterior carotid of the opposite side. 
From the ventral end of the first efferent branchial artery springs the mandibular 
artery (figs. 2, 6, and 10, Mandib. A.), which extends upwards along the outer face 
of the hyoid arch and just internal to the mandible, thus running parallel to the 
efferent branchial arteries. Distally it breaks up into several branches at about 
the level of the pseudobranchial artery (fig. 10). In Callorhynchus the evidently 
homologous vessel (Plate 36, fig. 17, Mandib. A.,) anastomoses with the proximal 
end of the anterior carotid—which, in the absence of a pseudobranchia, springs 
directly from the first efferent branchial artery—and appears from its position and 
relations to represent the mandibular aortic arch. 
From the analogy of Callorhynchus it would seem, therefore, that the mandibular 
artery is to be looked upon as a part of the original mandibular aortic arch, the 
rest of the ventral portion of which, represented by the pseudobranchial artery, 
has acquired a secondary connexion, comparable to the transverse commissures 
(com. 2), with the first efferent branchial artery. Whether the anterior carotid, 
together with the anastomotic trunk w, has anything to do with the original con¬ 
nexion of the mandibular aortic arch with the dorsal aorta (mandibular epibranchial 
artery) it is of course impossible to decide from anatomical evidence alone. 
The following table shows what I conceive to be the relation of the arteries 
of the adult to the embryonic aortic arches :— 
In the Embryo. 
In the 
Adult. 
Dorsal Section. 
Ventral Section. 
1st Aortic arcli (mandibular) 
Commissure w (?), anterior 
carotid artery. 
Pseudobranchial artery. 
Mandibular artery. 
2nd Aortic arch (liyoidean) . 
Vessel y ; posterior carotid 
from origin to x. 
1st afferent branchial artery. 
1st efferent branchial artery. 
3rd Aortic arch (1st branchial) . 
1st epibranchial artery . 
2nd efferent branchial artery. 
2nd afferent branchial artery. 
3rd efferent branchial artery. 
4t7i Aortic arch (2nd branchial) . 
2nd epibranchial artery 
4th efferent branchial artery. 
3rd afferent branchial artery. 
5th efferent branchial artery. 
5th Aortic arch (3rd branchial) 
3rd epibranchial artery. . . 
6th efferent branchial artery. 
4th afferent branchial artery. 
7th efferent branchial artery. 
6th Aortic arch (4th branchial) . 
4th epibranchial artery 
8th efferent branchial artery. 
5th afferent branchial artery. 
9th efferent branchial artery. 
4 t 2 
