272 PROF. OWEN ON THE ANATOMY 
margins of the diaphragm between the heart and liver, to have completely separated 
from the thorax the proper abdominal viscera, as in the Mammalia ; for, as will be pre- 
sently described, the respiratory organs are confined entirely to the thoraa. 
The heart presents the usual ornithic form of a somewhat elongated cone, terminated 
by an obtuse rounded apex, produced beyond the projection formed by the right ven- 
tricle. The pericardium, after being reflected upon the origins of the great vessels, 
passes directly from the peripheral surface of the auricles upon the ventricles, so that 
there are no freely projecting auricular appendages. In one Apteryx I found much fat 
developed in the angle between the auricles and ventricles, beneath the pericardium. 
The right auricle appeared, when distended, of an uncommon size. The three veins 
terminated in it in the usual manner, but the inferior cava has a much greater relative 
capacity than either of the superior cave, in consequence of these having to return to 
the heart little more than the proportion of venous blood brought back by the jugular 
and internal thoracic veins in other birds. 
The auricles of the heart do not present any peculiarity of structure which is not met 
with in other birds ; the resemblance to the Hmeu in the disposition of the valves of the 
right auricle is very close. The great inferior cava, (Pl. LII. 6, fig. 3,) the trunk of which 
is extremely short, opens into the sinus venosus close to the termination of the left superior 
cava (c, fig. 3.) ; the intervening membrane is slightly produced in a valvular form: the 
coronary vein of the heart terminates in the left superior cava, just before it opens into 
the auricle. The right superior cava (d, fig. 3.) opens as usual into the upper part of the 
sinus. The tunics of the superior cave are remarkably strong. The sinus is divided, 
as in other birds, from the proper auricle by two semilunar valves, one large and an- 
terior, the other smaller and posterior (e and f, fig. 3.). The lower horn of each valve 
is fixed to the floor of the auricle, the upper or anterior horn of the anterior valve is 
attached to a strong muscular column, which traverses the upper and anterior wall of 
the auricle ; the extremity of the posterior valve is in like manner continued into a 
muscular band from the back part of the auricle. From these attachments it is obvious 
that the valves, during the action of the muscular parietes of the auricle, will be drawn 
together, and their power to resist regurgitation into the sinus will be increased, as 
the action of the muscles to overcome the resistance of the contents of the auricle is 
greater. 
The posterior valve which forms part of the boundary of the foramen ovale seems to 
be represented in Mammalia by the muscular ridge called the annulus ovalis ; the ante- 
rior valve is obviously the analogue of that called Eustachian in Man and Mammalia. 
The principal deviation from the ornithic type of the structure of the heart is pre- 
sented in the valve at the entry into the right ventricle (Pl. LII. g, fig. 3,). This is 
characterized in birds by its muscularity and its free semilunar margin. In the Apteryr 
it is relatively thinner, and in some parts semitransparent and nearly membranous: a 
process moreover extends from the middle of its free margin, which process is attached 
