276 DESCRIPTION OF THE PLATES. 



FIG. 2. Heart, with ductus Cuvieri and base of the ventral aorta of Raja Batis. The walls of 

 the several sections of the heart have been removed in part to show points of internal structure. 

 Ventral view. From a specimen. 



a. Ventricle, single as in all Pisces, Amphibia and Reptilia, with the 



exception of the Crocodile. The walls are thick, and the inner 

 surface shows numerous bands of muscular tissue (columnae carneae). 

 The cavity is curved and the entrance into it from the auricle is 

 guarded by two large membranous valves, seen in the right upper 

 corner of the diagram, the left corner in the natural position. 



b. Conus or bulbus arteriosus. The aperture of the ventricle leading into 



it lies on the opposite side to the auricular aperture. Its walls are 

 thick, composed of striated muscular tissue, and it is rhythmically 

 contractile. Its cavity contains three longitudinal rows of pocket- 

 shaped membranous valves, four in each row. The distal valve in 

 each row is the largest. The number of valves in each row appear 

 to vary in the different species of Rays. 



The conus must be regarded as a part of the ventricle. It is present 

 in Ganoidei and Dipnoi among Pisces, and in Amphibia. The number of 

 rows of valves and of valves in each row that it contains is very variable. 

 The distal valves persist and form the valves that guard the entrance to 

 the aorta in those Vertebrata in which the conus is not present as a 

 separate division of the heart. 



c. The line points to the left posterior innominate artery. It and its 



homologue on the other side of the body spring from the base of the 

 median aorta. The aorta is composed chiefly of membranous tissue, 

 and the muscular tissue present in its walls is un'striped. (Cf. Fig. i, 

 b and c). 



d. d. The right and left pouches of the large thin-walled auricle. This 



structure is single as in all Pisces except Dipnoi. Its walls are thin 

 and its muscles form a network of trabeculae. 



e. e. The right and left ductus Cuvieri. These two vessels bring back to 



the heart the venous blood of the whole body. They fuse in the 

 middle line posteriorly to the auricle forming the sinus venosus. The 

 aperture of this sinus into the auricle is guarded by two membranous 

 valves. 

 The cavity of the whole heart makes an S -shaped curve, much more 



distinct in some Sharks than in the Ray. This curve is an embryonic 



feature in other Vertebrata. 



FIG. 3. Brain, with the roots of the chief nerves of Raja Batis. Dorsal view. From a 

 specimen. 



a. The Lobi olfactorii connected by long olfactory tracts to the cerebral 

 lobes from which they are outgrowths. Each lobe is lengthened out 



