BLOOD-VESSELS OF MUSTELUS ANTARCTICUS. 
69 7 
The hypobranchial artery. 
Figured, but not named, by Monro (16). 
Ventrale Verlangerungen der Venen des ziveiten Kiemensackes (in 
Raja), IIyrtl (11). 
Grosse branche anastomotique, &c., Milne Edwards (14). 
Hypobranchial arteries, Parker (23). 
This remarkable system of arteries, forming an anastomosis between the efferent 
branchial and the subclavian arteries, was, as far as I am aware, first described by 
Monro in the skate, and was afterwards more accurately figured in the same type by 
Hyrtl. 1 have seen no account of any such vessels in Selachians ; both Muller and 
Milne Edwards write as if they were confined to the Batoidei, and no mention of 
them is made in any of the text-books I have had the opportunity of consulting. 
After separating from the brachial, the hypobranchial artery (Plate 34, fig. 2, 
Hypbr. A.) gives off a branch to the lateral body muscles, and then passes forwards 
and inwards through the ventral wall of the pericardial cavity, finally uniting with 
its fellow of the opposite side at about the level of the junction of the ventricle with 
the conus arteriosus. About midway between this junction and its origin from the 
subclavian each hypobranchial sends off a small anterior lateral artery (figs. 1 and 2, 
Ant. lat. A.), which accompanies the lateral vein and helps to supply the anterior body 
muscles. 
The median trunk formed by the union of the paired hypobranchial arteries passes 
forwards and upwards amongst the muscles of the throat until it reaches the ventral 
aorta about 2 cm. cephalad of its origin from the conus arteriosus ; it then breaks 
up (fig. 2) into a simple plexus, which is united by two pairs of commissural trunks 
with the longitudinal vessels (com. 1) uniting the ventral ends of the efferent 
branchial arteries. The anterior of these (com. 3) arises between the fourth and fifth 
efferent arteries and joins the median hypobranchial immediately ventrad of the origin 
of the third afferent branchial artery from the ventral aorta. The posterior commis¬ 
sure (com. 4) arises between the sixth and seventh efferent arteries and joins the hypo¬ 
branchial at the level of the origin of the fourth and fifth afferent arteries. Cephalad 
of the anterior of these commissural trunks the median hypobranchial artery is con¬ 
tinued forwards as a slender vessel, which, at the level of the anterior end of the 
ventral aorta, breaks up into a number of branches distributed to the M. coraco- 
mandibularis. 
The coronary arteries 
(Plate 34, fig. 2, Cor. A.) are two in number, and arise from the azygos hypo¬ 
branchial artery close to the posterior pair of commissures (com. 4) from the efferent 
branchial arteries. The two coronaries pass backwards along the ventral face of the 
conus arteriosus, the right soon dividing into two, and branch out over the ventricle. 
MDCCCLXXXVl. 4 U 
