272 
PROFESSOR D. WATERSTON ON 
The proximal conical portion of the right ventricle is continued uninterruptedly 
into a distal tubular portion, on which an almost vertical furrow, lying on the right 
side, forms an external constriction corresponding to an internal division of the 
lumen. The portion behind the constriction contains the ascending aorta, and that 
in front the infundibulum leading to the pulmonary artery. 
Table IV. 
Dimensions of Heart of S4. x 100. 
Vertical height . . 
Transverse width, left ventricle . 
,, ,, right „ 
Dorso-ventral width, atria (middle) 
Left ventricle 
Right ,, 
,, venous ostium 
Thickness of wall, compact 
Interventricular opening 
Distance from apex 
200 mm. 
125 „ 
125 „ 
112 „ 
205 „ 
155 „ 
45 „ x 15. 
25 „ 
20 ,, x 15 mm. 
120 „ 
Internal Structure. — The incorporation of the sinus into the atrium has advanced, 
and the position and attachments of the venous valves and of the atrial septum are 
of great interest (text-figs. 8, 9, and 10). 
The venous valves stretch from the dorsal to the ventral wall of the atrium both 
orally and caudally, and they enclose between them a central narrow slit-like 
chamber which receives blood from the venae cavse and the coronary sinus. On each 
side is the widely dilated atrium proper. The central chamber communicates with 
each of these by a small somewhat oval opening, and they in turn lead into the 
ventricle on each side. This central chamber may be termed the sinu-atrial chamber. 
The venous valves meet and blend with one another in both the roof and floor of 
the chamber. The vena cava superior opens by a narrow orifice through the upper 
part of its dorsal wall, and the vena cava inferior and the coronary sinus open in the 
floor separately, the latter far forward. 
The right venous ostium lies on the right side of the base of the right venous valve. 
Closely blended with the left venous valve is the septum primum atriorum. 
From the left side of the septum primum the wall of the left atrium slopes 
sharply to the left ostium. 
The septum primum forms a complete ring round the interior of the circumfer- 
ence of the atrium, but the foramen ovale secundum is so large that nowhere is the 
septum of any considerable height. The septum and the venous valves are shown in 
Plate-fig. 10 viewed from the left side. It is deepest in the ventral inferior portion 
and very shallow indeed on the dorsal wall, and at its dorsal and inferior attachments 
it is largely blended with the left venous valve. 
The single large pulmonary vein opens into the left atrium immediately to the 
left side of the septum primum. 
