PROGRESS OF VETERINARY SCIENCE AND ART. 529 
ventricle. In the latter was the rudiment of a septum, and 
towards its base were four openings — two auricular, and two 
lesser arterial ones, whence emerged the aorta and pulmonary 
artery. The tricuspid valves are replaced by a broad and 
slender membrane, springing from the upper part of the 
ventricle, near the anterior border of the arterial apertures, 
connected with the parietes of the ventricle by a few weak 
tendinous filaments. The position and sphere of motion of 
this membrane prove that it performed the functions of the 
tricuspid valve. A membrane turned in the opposite sense, 
but otherwise similarly disposed, exists in the place of the 
mitral valve. The arterial openings close to each other are 
guarded by delicate semilunar folds, just as in health. 
The ventricle is the same thickness all over, and that it is 
formed by the fusion of the two can only be determined by 
the existence of an external groove and of the internal rudi- 
mentary septum. The right auricle which receives the two 
venae cavae is flabby, only slightly muscular, and has not the 
internal reticular appearance that in the normal state is seen 
as due to the musculi pectinati. The left auricle is of normal 
bulk and structure, but is lengthened out; it is only the 
auricular appendage that protrudes through the sternal aper- 
ture; the sinus venosus is prolonged midway into the thorax, 
and there receives the great pulmonary veins. The pulmonary 
artery and aorta are joined together by areolar tissue ; they 
have a free passage through the sternal aperture and pass 
upwards, slightly inclining forwards into the thorax, towards 
the upper part of which they are joined by the ductus arte- 
riosus ; the pulmonary artery then bifurcates. With reference 
to the veins, the most singular condition was that of an 
anastomosis between the anterior and posterior venae cavae, 
so that only one trunk entered the right auricle ; at the 
aperture of this common trunk was no Eustachian valve. 
Between the auricles was a large foramen ovale without valve. 
It is very evident that the commingling of arterial and venous 
blood in the heart was complete, and this mixed blood it was 
that entered both systemic and pulmonic arterial systems, 
accounting for the cyanosis, for the disturbance of the respi- 
ration, and, indeed, for all the morbid phenomena that caused 
the speedy death of the animal. 
The heart, arrested in its development, had in this calf 
the construction of the heart of reptiles. The central organ 
of circulation in a tortoise only differs from the one above 
described in the auricular septum being impervious and in 
the absence of ductus arteriosus. Two causes, then, says 
Alessandrini, have chiefly contributed to the formation of 
xxix. 68 
