804 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION, 



Figs. 19, 20, 21, 22, 23, and 24, Show the Structure of the Semilunar Valves in the Human Pul- 

 monary Artery. (See pp. 772, 773, 774, 775.) 



Fig. 25. Human Semilunar Valve distended with plaster of Paris, and one of the segments (g) re- 

 moved, to show the precise shape of the lunulse, or opposing surfaces (6 b'), between which 

 imioa takes place when the valve is in action, (See pp. 776, 777.) 



Fig. 26. Shows the spiral relation of the Sinuses of Vals.vlva to the segments (y w x) of the semi- 

 lunar valve in the Human Pulmonary Artery, and how the segments are spirally wedged 

 into each other, and fixed by six non-symmetrical semilunar surfaces, to form three per- 

 pendicular crescentic walls [r s o). Seen from beneath. (See pp. 776, 777.) 



Fig. 27. Shows the Semilunar Valves in the Heart of the Sheep {y w x) distended with plaster of Paris, 

 or as they appear in action, together with the spiral nature of that action. (See pp. 776, 

 777.) 



Fig. 28. Shows the same in the Aorta {y w x) of the Human Heart, and in addition, the bifid nature 

 of the musculi papillares (a 6, cc/), and the distribution of the chord* tendinese to both 

 segments of the mitral valve (inn). (See pp. 776, 777, 787, 788, 789.) 



Fig. 29. Vertical Section carried through the Aorta and through the middle of one of the segments 

 of the Semilunar Valve of the Whale. Shows the variation in the thickness of the vessel 

 (ce), and the structure of the semilunar valve (ars' o). (See pp. 770, 773, 774.) 



Fig. 30. Shows Arterial and Auriculo-ventricular Orifices, with their fibrous rings (x v n n'). (See 

 pp. 769, 770.) 



Fig. 31. Human Mitral Valve, Chordae tendineae, and Musculi papillares inverted. Shows the bifid 

 nature of the musculi papillares (a 6), and the threefold distribution of the chordaa ten- 

 dinefE (s). (See pp. 786, 787, 788, 788.) 



Fig. 32. Shows Structm-e of the Mitral Valve in the Sheep. (See pp. 786, 787, 788, 789.) 



Fig. 33. Anterior Segment of Human Mitral Valve. Shows the threefold distribution of the chordse 

 tendinese, from above downwards, and from the mesial line towards the margin of the 

 segments. (See pp. 786, 787, 788, 789.) 



Fig. 34. Example of Mitral Valve in the Right Ventricle of the Human Heart. (See pp. 789, 790, 

 791.) 



Fig. 35. Vertical Section, carried through the aorta (a a') semilunar valve (s s' s"), left auricle 

 (d d', y y'), the segments of the mitral valve (w m', n vi), and the left ventricle (y v'), of the 

 Human Heart. Shows the greater thickness of the aorta, where the segments of the semi- 

 lunar valve unite above (b b', c c'), and its greater tenuity behind the centre of each seg- 

 ment (o) ; also how a portion of the aorta [p) is continued into the larger or anterior seg- 

 ment of the mitral valve (m m). It also shows the relation of the left auricle (y «/', d d') 

 to the aorta (a a'), mitral valve (m m', n n'), and left ventricle (v v'). 



rr, Openings of coronary arteries. 

 nn'. Segments of semilunar valve uniting above. 



X x\ e e'. Auricle terminating by wedge-shaped process in mitral valve. 

 z -j', Left coronary artery. 



1 1' t". Convex, or attached borders of segments of semilunar valve. 

 g, Septal wall of left ventricle. 

 A A', Chordse tendinese. 

 i i', Musculi papillares. 



ly'. Apex of left ventricle. (See pp. 770, 771). 

 Fig. 36. Left Ventricle of Human Heart laid open to show the semilunar (ss') and mitral (yi) valves 

 in situ. (See pp. 770, 771.) 



Plate XXIX. 



Fig. 37. Portion of Heart of Sturgeon. Shows auriculo-ventricular valve (a) with three chordse 



tendine^ (6) proceeding from it. (See p. 781.) 

 Fig. 38. Ventricle and Bulbus Arteriosus of Skate laid open. Shows several rows of semilunar 



valves (a b c) increasing in size in a direction from below upwards. (See p. 779.) 



