770 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION 



Plate XXVIII. figure 30, taken from a photograpli of a boiled heart, consists, 

 as was shown by Reid, of three convex portions (rst). Each convex portion is 

 directed from above downwards, and from without inwards, and as it unites 

 above with that next to it, the two when taken together form a conical-shaped 

 prominence {x), which is adapted to one of the three triangular-shaped inter- 

 spaces occurring between the segments of the valve (Plate XXVIII. fig. 17 h). 

 The arterial rings are therefore placed obliquely, the under surface, which gives 

 attachment to many of the fibres of the ventricles anteriorly (Plate XXVIII. fig. 

 30 dd'), resting on the rounded oblique border of the ventricular walls (Plate 

 XXVIII. fig. 17 ^). The ring surrounding the pulmonary artery, as was pointed 

 out by Reid, is broader, but not quite so thick as that surrounding the aorta, 

 and both are admirably adapted for the reception of the large vessels which, 

 as was shown by that author, originate in three festooned borders. These 

 borders, I am inclined to think, consist of two parts, — an outer (Plate XXVIII. 

 fig. 17 r ?•'), composed of the outer, and a small portion of the central layer of 

 either the aorta or pulmonary artery; and an inner (t), composed principally 

 of the central and inner layers. The outer border (Plate XXVIII. fig. 18 r), 

 which is the thinner of the two, is attached to the supei'ior and outer margin 

 of one or other of the fibrous rings {g), chiefly by the serous membranes ; the 

 inner (Plate XXVIII. fig. 17 t), M'hich projects further in a direction from 

 above downwards, and corresponds to the thickened convex border of the seg- 

 ments (s), to the formation of which it contributes, being attached to the 

 inferior and inner margin {g'). These points are well seen, when a vertical 

 section is made of the aorta or pulmonary artery between the segments com- 

 posing the semilunar valves. In such a section (Plate XXVIII. fig. 17), the 

 vessels are observed to be thickened in a direction from above downwards, 

 the thickening beginning at the point where the segments meet above {h\ and 

 gradually increasing until the vessels bifurcate {r' t). The reverse of this 

 holds true of those portions of the vessels which enter into the formation of 

 the sinuses of Valsalva (Plate XXVIII. fig. 18 «), these being unusually thin, 

 particularly where attached (?•).* As the thickened portions of the vessels 

 correspond to the fixed margins of the segments (Plate XXVIII. figs. 17 and 

 35 htn), and extend between them in an arched direction above (c), they 

 give the precise boundaries of the sinuses of Valsalva (Plate XXVIII. figs. 

 17 and 18 d)^ and furnish the segments with three fibrous frameworks analogous, 

 in some respects, to the thickenings which occur in similar situations in the 

 veins. These frameworks extend for a short distance into the segments (Plate 

 XXVIII. fig. 17 5, and fig. 36 n), and assist not only in affording the segments 



* The several points adverted to are seen to advantage in the whale (Physalus antiquorum, 

 Gray), the aorta of which I had an opportunity of dissecting for the Museum of the Royal College 

 of Surgeons of England. 



