38 ALLEN 
anastomoses with the facialis-mandibularis branch of the exter- 
nal carotid forming the mandibular artery; the pharynx artery 
(Pl. II, fig. 12; Phar.A.) for the ventral branchial muscles, 
from which the coronary artery (Pls. I and II, figs. 1 and 12; 
Cor.A.) arises; the ventral artery (Pls. I and II, figs. 1 and 12; 
Ven.A.) for the ventral or pelvic fins and the ventral body 
walls; and several smaller arteries, which will be described in 
detail further on. Dorsally the efferent vessels send off anteri- 
orly the common carotid arteries (fig. 1; C.Car.A.), which 
supply the face, orbit, nose, and brain; and posteriorly the 
efferent branchial vessels unite in forming the c@/zaco-mesen- 
teric artery (Pl. I, figs. 1 and 5; Coe.Mes.A.) for the viscera ; 
the subclavian arteries (figs. I and 5; Sub.A.) for the pectoral 
fins; and the dorsal aorta (figs. 1 and 5, D.Ao.) for the body 
walls, tail, kidney, and reproductive organs. The union of 
these efferent branchial vessels to form the internal carotids 
anteriorly and the dorsal aorta posteriorly, forms what is known 
as the czrculus cephalicus. 
V. Hears. 
This organ, which is inclosed in the triangular cardiac space, 
lies in the ventro-median line directly cephalad of the pectoral 
arch. The pharnyx forms the roof of this cavity, the thick sterno- 
hyoideus muscle the floor, and together with the pharyngo-clav- 
icularis internus muscles it makes up the lateral walls; while 
the aponeurotic membrane forms the posterior wall that sep- 
aratés the cardiac cavity from the visceral cavity. This cham- 
ber is lined with the pericardium, which, like the peritoneum, 
consists of a parietal and visceral layer; the former lines the 
cavity and the latter loosely envelops the heart, being attached 
anteriorly to the ventral aorta in the region of the first afferent 
branchial vessels and posteriorly to the dorsal and ventral wall 
of the precava. The space between the parietal and visceral 
layers is known as the outer pericardial cavity or pericardial 
lymphatic sinus, for it is in direct communication with the lym- 
phatics ; while the space between the heart and the visceral layer 
is known as the inner pericardial or pericardial cavity proper. 
No connections were noticed between these 2 cavities. 
As in the other vertebrates the heart is the center of activity , 
