RATA. 317 
The feart lies in the pericardium. It has two chambers 
a thick-walled ven¢ricle and a larger thin-walled auricle lying 
dorsal to it. The ventricle leads forwards 
out of the pericardium as the conus arteriosus 
containing valves, beyond which it is continued 
as the dvanchial artery.* The auricle receives blood from 
a thin-walled triangular séwws venosus formed from the 
swollen termination of the main veins. 
The branchial.artery gives off a pair of posterior in- 
nominates, which trifurcate into three afferent branchials 
supplying the three posterior pairs of gills. The branchial 
artery runs forward and terminates just behind the lower jaw, 
near a small ductless thyroid gland. Here it diverges into two 
anterior innominates, each of which bifurcates into two afferent 
branchials supplying the first two pairs of gills : this comprises 
the afferent branchial system. On contraction of the ven- 
tricle of the heart the blood passes forward to the gills, 
hence the skate’s heart is purely vespzratory. If the coracoid 
bar be now carefully removed, the sinus venosus will be seen 
to run downwards and outwards on each side to the fre- 
caval sinus, which communicates with a spacious /epatic 
sinus in connection with the liver and receives a jugular 
vein from the head, a /azeral vein (formed of a Ze/vic from 
the pelvic fin and a érachial from the pectoral fin) and 
a cardinat vein from the posterior part of the body and 
kidneys. A median cauda/ vein from the tail diverges into 
a pair of renal portals to the kidneys, in which the veins 
break up into capillaries. A skate has therefore a renal 
portal system as well as a hepatic portal. 
If the ventral wall of the pharynx and the skin of the roof 
of the pharynx be removed, the efferent branchial system is 
exposed (Plate II). It consists of five efferent branchials 
leading from the gills towards the middle line and back- 
wards. The two first unite into one, as also do the two 
last ; hence three arteries are produced which then unite to 
form the dorsal aorta. From the first efferent branchial on 
each side runs forward a carotid, dividing into ¢xternal 
carotid to the brain and external carotid to the head. The 
dorsal aorta gives off paired szbclavians to the pectoral fins, 
and is continued along the dorsal line under the vertebral 
* Often termed the Ventral Aorta. 
Blood- 
Vascular. 
