288 



THE ARTICULATIONS 



continued onward to the bases of the second, third, and fourth rnetatarsal bones. 

 This ligament crosses the groove on the under surface of the cuboid bone, convert- 

 ing it into a canal for the passage of the tendon of the Peroneus longus. 



The Short Calcaneo-cuboid (Short Plantar) Ligament lies nearer to the bones 

 than the preceding, from Avhich it is separated by a little areolar tissue. It is 

 exceedingly broad, about an inch in length, and extends from the tubercle and the 

 depression in front of it, on the fore part of the under surface of the os calcis, to 

 the inferior surface of the cuboid bone behind the peroneal groove. 



Synovial Membrane. The synovial membrane in this joint is distinct. It 

 lines the inner surface of the ligaments. 



Actions. The movements permitted between the os calcis and cuboid are 

 limited to a slight gliding upon each other. 



3. THE LIGAMENTS CONNECTING THE Os CALCIS AND NAVICULAR. 



Though these two bones do not directly articulate, they are connected together 

 by two ligaments : 



Superior or External Calcaneo-navicular. 

 Inferior or Internal Calcaneo-navicular. 



The Superior or External Calcaneo-navicular (Fig. 190) arises, as already men- 

 tioned, with the internal calcaneo-cuboid in the 

 deep hollow between the astragalus and os 

 calcis; it passes forward from the upper surface 

 of the anterior extremity of the os calcis to the 

 outer side of the navicular bone. These two 

 ligaments resemble the letter Y, being blended 

 together behind, but separated in front. 



The Inferior or Internal Calcaneo-navicular 

 (Fig. 192) is by far the larger and stronger of 

 the two ligaments between these bones ; it is 

 a broad and thick band of fibres, which passes 

 forward and inward from the anterior margin 

 of the sustentaculum tali of the os calcis to the 

 under surface of the navicular bone. This 

 ligament not only serves to connect the os 

 calcis and navicular, but supports the head of 

 the astragalus, forming part of the articular 

 cavity in which it is received. The upper 

 surface presents a fibro-cartilaginous facet, 

 lined by the synovial membrane continued 

 from the anterior calcaneo-astragaloid articu- 

 lation, upon which a portion of the head of 

 the astragalus rests. Its under surface is in 

 contact with the tendon of the Tibialis posticus 

 muscle ; l its inner border is blended with the 

 fore part of the Deltoid ligament, thus com- 

 pleting the socket for the head of the astragalus. 



Surgical Anatomy. The inferior caleaneo-nav- 

 icular ligament, by supporting the head of the astrag- 

 alus, is principally concerned in maintaining the arch 

 of the foot, and when it yields, the head of the astrag- 

 alus is pressed downward, inward, and forward by the 

 weight of the body, and the foot becomes flattened, 

 expanded, and turned outward, constituting the dis- 

 ease known as fiat-foot. This ligament contains a considerable amount of elastic fibre, so as to 



1 Mr. Hancock describes an extension of this ligament upward on the inner side of the foot, 

 which completes the socket of the joint in that direction (Lancet, 1866 vol. i., p. 618). 



FIG. 192. Ligaments of the plantar surface 

 of the foot. 



