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



XXVIII. fig. 84 mn, the distribution of the chordae tendinese (op) in the 

 segments is the same as that given when describing the bicuspid of the left 

 ventricle ; but when there are three principal segments, with as many or 

 more accessory segments, the distribution is varied to meet the exigencies of 

 the case ; there being a tendency in each of the chordse tendinese to divide into 

 three ; one of the chords so divided being inserted by one of its slips into the 

 mesial line of the segment at the base posteriorly ; by another into the margin 

 of the segment, likewise at the base ; and by the remaining slip into a point 

 intermediate between the mesial line and the margin. Other chords, similarly 

 divided, are inserted at intervals in a direction from above downwards, or from base 

 to apex (Plate XXVIII. fig. 34 o), the insertions in each case proceeding from the 

 mesial line towards the margin. In some instances, though more rarely, a mixed 

 arrangement prevails ; the insertions of the three tendinous slips running from 

 the mesial line of the segment towards the margin, and from the base to the 

 apex indiscriminately ; but whatever the arrangement on the one side of a seg- 

 ment, it is, as a rule, the same on the other, so that one of the segments of a true 

 tricuspid valve is as symmetrical in its way as a segment of a bicuspid one. The 

 musculi papillares in the right ventricle of a typical heart, are two in number, as 

 in the left. When, therefore, the right auriculo-ventricular opening is closed by 

 a tricuspid valve, an additional origin is required for the chordse tendinese ; and 

 in such a case these chords spring from the two musculi papillares, and from the 

 right side of the septum behind the fleshy pons, either from a rudimentary 

 papillary muscle, or from carnese columniTe, or from the smooth wall of the sep- 

 tum. The number of papillary muscles in the right ventricle (and the same 

 remark applies to the left, although not to the same extent) vary somewhat ; the 

 two typical ones being frequently seen to bifurcate at their free extremities, 

 and others to spring up in their vicinity. On these occasions the origins of the 

 chordee tendinese are increased, but this does not materially affect their insertion, 

 which is remarkably uniform. The tricuspid valve, differs from the bicuspid as 

 regards actual strength, the segments being comparatively thinner. This deli- 

 cacy of structure, extends to the chordse tendinese and to the musculi papillares, 

 in fact, to everything pertaining to the right ventricle ; the walls of M'hich, as is 

 well known, are only half the thickness of those of the left ventricle. The com- 

 parative feebleness of the tricuspid valve, is no doubt traceable to the smaller 

 amount of force it is called upon to withstand, the pulmonic circulation being 

 less vigorous than the systemic. From the foregoing description, it will be seen, 

 that the chordse tendinese are inserted into every portion of the bicuspid (Plate 

 XXVIII. figs. 31, 32, and 38) and tricuspid valves; and as they freely decussate 

 with each other in all directions, by means of their terminal brush-shaped expan- 

 sions, and are of infinite variety as regards length and strength ; those at the base 

 and posterior aspect of each segment being long and exceeding strong ; while those 



