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 (Pis. I and II, figs, i and 12 ; 

 Cor. A.) arises ; the ventral artery (Pis. I and II, figs, i 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. Dors ally the efferent vessels send off anteri- 

 orly the common carotid arteries (fig. i ; C.Car.A.), which 

 supply the face, orbit, nose, and brain ; and posteriorly the 

 efferent branchial vessels unite in forming the coeliaco-mcsen- 

 teric artery (PL I, figs, i and 5 ; Cce.Mes.A.) for the viscera; 

 the subclavian arteries (figs, i and 5 ; Sub. A.) for the pectoral 

 fins; and the dorsal aorta (figs, i 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 posteriori}"", forms what is known 

 as the circidiis ccpJialicus. 



V. Heart. 



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- 

 arates 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 tlie heart is the center of activity , 



