Although there have been numerous articles concerning the anatomy of the atrioventricular valve in man, only a few publications have recorded the relationship between the chordae tendineae and the papillary muscles. The purpose of this paper is to study the relationship among the shape and size of the atrioventricular valve, the chordae tendineae and the papillary muscles. 50 subjects, as listed in Table 1, were analyzed by the Taniya-Hashimoto Method.
The results obtained were as follows:
1) The right atrioventricular valve was classified into two types: 33 cases (66%) of three irregularly shaped cusps, i. . type I, and 17 cases (34%) of four or five cusps, i. . type II.
2) The average circumference of the right atrioventricular orifice (ostium atrioventriculare dextrum) was 11.cm (.63.15.06cm) in type I and 12.19cm (.52.15.cm) in type H. There existed no significant difference in the circumference of the atrioventricular orifice between type I and II.
3) The average length of the cusp-fundus (the length of the fixed margin of the cusp) was as follows:
type I: anterior cusp…………4.13cm (2.03-6.cm)
posterior cusp…………3.62cm (1.21-.44cm)
septalcusp……………4.21cm (3.11-6.08cm)
type II: anterior cusp…………4.10cm (2.68-.42cm)
posterior cusp…………3.67cm (.94-.70cm)
septal cusp……………4.43cm (2.-6.53cm)
4) The average width of the cusp (the maximum distance between the apex and the fundus of the cusp) was as follows:
type I: anterior cusp…………1.86cm (1.26-2.29cm)
posterior cusp…………1.62cm (.62-2.94cm)
septal cusp……………1.76cm (1.15-2.72 cm)
type II: anterior cusp…………1.cm (1.40-2.34cm)
posterior cusp…………1.72cm (.94-2.42cm)
septal cusp……………1.84cm (1.14-2.53cm)
The length or width of the cusp in type I was similar to that in type II.
) The papillary muscles consisted of five groups, which were named the anterior, postlateral, postmedial, postseptal and septal muscles. The average number of the papillary muscles per right ventricle was .7 (2...). The chordae tendineae from the anterior papillarymuscles were attached to the anterior and posterior cusps and those from the postlateral and postmedial muscles were attached to the posterior and septal cusps. The chordae tendineae from the postseptal muscles were linked only to the septal cusp and those from the septal muscles were connected to the septal and anterior cusps.
6) The average number of the stems of the chordae tendineae from the papillary muscles were as follows:
From the anterior papillary muscles………7.2 (2.-14.)
the postlateral papillary muscles……3. (1.-.)
the postmedial papillary muscles……4. (1.-.) the postseptal papillary muscles……4. (1.-13.) the septal papillary muscles……….7 (2.-12.)
The average n umber of the stems of the chordae tendineae per right ventricle was 24.4 (16.-35.).
7) The tip of the chordae tendineae are attached to the fixed margin of the valve cusp, i. . type A, to the ventricular surface, i. . type B and to the free margin, i. . type . The average number of them were 23.4 (14.-32.) in type A, 19.2 (4.-37.) in type B and 68.1 (31.-105.) in type . The average number of the apexes of the chordae tendineae per right ventricle was 110.7 (53.-166.).
) The average number of the chordae tendineae for the anterior cusp was 34. (12.-64.), for the posterior cusp 30. (.-65.) and for the septal cusp 45.3 (23.-68.).

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To determine the position of the anteriorly displaced articular disc, we examined temporomandibular joints by magnetic resonance imaging (MRI) in 54 patients with unilateral temporomandibular joint dysfunction. MRI was done before conservative therapy in the occlusal and maximal open-mouth position. We drew a straight line connecting the lowest point of the articular eminence (point A) and the highest point of the external acoustic pore (point ) by tracing the sagittal view on MRI. On the standard A- line, points B', ', and D' were sought by dropping perpendicular lines from the deepest point of the glenoid fossa (point B), the highest point of the condylar head (point ), and the most posterior point of the articular disc (point D). We then determined the sagittal position of the articular disc in the glenoid fossa by measuring the distances ' and 'D' and sought the correlation between these distances and clinical findings. The results were as follows. 1. The distance ' in 33 patients with MRI-defined irreversible displacement of the disc was shorter than that in 10 patients with reversible displacement (3.7±1.mm vs 6.±2.mm, p<.0001). In contrast, the distance 'D' in the former was longer than that in the latter (6.±1.7mm vs 3.4±1.mm, P<.0001). Of 29 discs displaced anteriorly less than mm in distance 'D', 19 (66%) had reversible or no displacement. However, 23 (%) of 25 discs displaced more than mm in distance 'D' had irreversible displacement. 2. Disc deformity and abnormal signal intensity bands in the condylar head closely correlated with distances ' and 'D'. In 17 patients without disc deformity, mean ' and 'D' distances were .± 2.7mm and .2± 2.mm, respectively. In 19 and 18 patients with mild to moderate and severe deformity, the mean '('D') distances were .4±1.mm (4.±1.6mm) and 2.7±1.mm (6.±1.mm), respectively. 3. Although distance ' and 'D' did not correlate with clinical symptoms, the degree of anterior disc displacement correlated with the therapeutic effect of conservative therapy. The mean ' distance (7.3±3.7mm) in 15 patients with a complete response to conservative therapy was longer than that (3.4±1.4mm) in patients with no improvement. These results indicate that the sagittal position of the articular disc can be determined by MRI and that successful conservative therapy is unlikely if anterior disc displacement extends beyond mm from the top of the condylar head, often resulting in irreversible displacement.

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