THE ASTRAGALUS. 2355 
Variations.—The anterior is sometimes separated from the middle caleanean facet by a non- 
articular furrow. The posterior external tubercle, often largely developed, is occasionally (2°7 
al 
B 
Fic, 1/5.—THE RicHT ASTRAGALUS. 
A, Upper Surface. B, Under Surface. 
1. GROOVE FOR FLEX. LONG. HALLUCIS. 9, FOR ARTICULATION WITH EXTERNAL 14. FoR ARTICULATION WITH NAVI- 
2. INTERNAL TUBERCLE. MALLEOLUS. CULAR. 
3. TROCHLEAR SURFACE FOR TIBIA. 10. SURFACE AGAINST WHICH THE 15, SURFACE RESTING ON INFERIOR 
4. Bopy. INFERIOR TIBIO-FIBULAR LIGA- CALCANEO-NAVICULAR LIGA- 
5. FOR ARTICULATION WITH INTERNAL MENT RESTS. MENT. 
MALLEOLUS. 11. EXTERNAL TUBERCLE. 16. INTEROSSEOUS GROOVE. 
6. HEAD. 12. EXTERNAL TUBERCLE. 17. INTERNAL TUBERCLE. 
7. FOR ARTICULATION WITH NAVICULAR. 13. POSTERIOR, MIDDLE, AND ANTERIOR 18. GROOVE FOR FLEXOR LONGUS 
8. NECK. FACETS FOR OS CALCIS. HALLUCIS. 
per cent) a separate ossicle forming what is known as the os trigonum (Bardeleben) ; or it may be 
united to the body of the astragalus by a distinct synchondrosis. A smooth articular surface may 
occasionally be found on the outer side of the upper surface of the neck. This is a pressure facet 
A Fic. 176.—THE RIGHT ASTRAGALUS. B 
A, As seen from the Outer Side. B, As seen from the Inner Side. 
1. EXTERNAL TUBERCLE. 10. INTEROSSEOUS GROOVE. 18. FORARTICULATION WITH INTERNAL 
2. GROOVE FOR FLEXOR LONGUS 11. ANTERIOR, MIDDLE, AND MALLEOLUS. 
HALLUCIS. . POSTERIOR FACETS FOR OS 19. Bony. 
3, INTERNAL TUBERCLE. CALCIS. 20. IMPRESSION FOR INTERNAL 
4. SURFACE AGAINST WHICH THE 12. Bopy. LATERAL LIGAMENT. 
INFERIOR TIBIO-FIBULAR LIGA- 13. SURFACE RESTING ON INTERNAL 21. INTERNAL TUBERCLE. 
MENT RESTS. CALCANEO - NAVICULAR LIGA- 22. GROOVE FOR FLEXOR LONGUS 
5. TROCHLEA FOR TIBIA. MENT. HALLUCIS. 
6. FoR ARTICULATION WITH 14. FoR ARTICULATION WITH NAVI- 23. EXTERNAL TUBERCLE. 
EXTERNAL MALLEOLUS. CULAR. 24. INTEROSSEOUS GROOVE. 
7. NECK. 8. Heap. 15. Heap. 25. POSTERIOR AND MIDDLE FACETS 
9. FoR ARTICULATION WITH 16. NECK. FOR OS CALCIS. 
NAVICULAR. 17. TROCHLEA FOR TIBIA. 
dependent on the frequent use of the ankle-joint in a condition of extreme flexion, and is caused 
by the opposition of the bone against the anterior edge of the lower end of the tibia. 
