THE DEVELOPMENT OF THE HEART IN MAN. 
265 
The right ventricle and its tubular continuation have the same flask shape 
noted in Si. 
Internal Structure. — Sinus venosus . — The right horn of the sinus venosus 
forms a chamber lying near the dorsal right corner of the atrium, and marked off 
from it externally by a vertical groove extending between the right margins of the 
venae cavae superior and inferior. The superior vena cava (right duct of Cuvier) 
opens into it high up on the dorsal wall, while the vena cava inferior and the trans- 
verse portion of the sinus venosus open into its floor ; between the latter two orifices 
is a small ridge. 
Sinu-atrial Junction t — The venous valves are much larger than in the former 
specimen, the right one particularly so, and it projects so far into the atrium 
as almost entirely to cut off the portion on its right from that on its left side. 
Along the floor of the atrium it extends as far as to the cushions of the 
atrial canal (text-fig. 4, and Plate-fig. 6). 
The left venous valve is shorter, but it also is prolonged for some distance along 
the floor of the atrium. Orally it blends with the right valve and forms a large 
“ tensor valvulse.” 
The orifice between the two valves is a vertical slit. The right venous valve 
shows again a recognisable difference in structure from the remainder of the heart 
wall, and is loose in texture. 
Atrium . — A wide bay on the outer surface of the roof of the atrium corresponds 
to the upper attachment of the septum primum. 
Table III. 
Dimensions of Model of the Heart of Bl. x 100 
Vertical height . 
Atrium, transverse width I 
’ l left 
,, vertical height 
Sinu-atrial orifice, vertical height 
Right venous valve, depth 
Left ,, ,, 
130 mm. 
100 
90 „ 
140 „ 
50 „ 
65 „ 
20 „ 
F. ovale primum still present, diameter . . 10 „ 
„ secundum, vertically . . . . 25 „ 
Distance between right and left venous orifices . . 42 ,, 
Ventricle, left, vertical height .... 105 „ 
„ ,, transverse width . . . 90 ,, 
„ „ thickness of wall . . . 40-60 ,, 
,, right, transverse width . . . . 90 ,, 
„ „ vertical height (conical portion) . . 65 ,, 
,, „ thickness of wall . . . 25 ,, 
Interventricular foramen, diameter . . . . 35 ,, 
„ ,, vertically .... similar. 
Distance of interventricular foramen from interventricular cleft 75 mm. 
Right and left venous valves united caudally and orally. 
TRANS, ROY. SOC. EDIN., VOL. LII, PART II (NO. 12). 
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