360 SYNDESMOLOGY 



Movements. The only movements permitted in the joints of the digits are flexion and exten- 

 sion; these movements are more extensive between the first and second phalanges than between 

 the second and third. The amount of flexion is very considerable, but extension is limited by the 

 plantar and collateral ligaments. 



Arches of the Foot. 



In order to allow it to support the weight of the body in the erect posture with 

 the least expenditure of material, the foot is constructed of a series of arches 

 formed by the tarsal and metatarsal bones, and strengthened by the ligaments 

 and tendons of the foot. 



The main arches are the antero-posterior arches, which may, for descriptive 

 purposes, be regarded as divisible into two types a medial and a lateral. The 

 medial arch (see Fig. 290, page 276) is made up by the calcaneus, the talus, the 

 navicular, the three cuneiforms, and the first, second, and third metatarsals. Its 

 summit is at the superior articular surface of the talus, and its two extremities or 

 piers, on which it rests in standing, are the tuberosity on the plantar surface of 

 the calcaneus posteriorly and the heads of the first, second, and third metatarsal 

 bones anteriorly. The chief characteristic of this arch is its elasticity, due to its 

 height and to the number of small joints between its component parts. Its weakest 

 part, i. e., the part most liable to yield from overpressure, is the joint between 

 the talus and navicular, but this portion is braced by the plantar calcaneonavicular 

 ligament, which is elastic and is thus able to quickly restore the arch to its pristine 

 condition when the disturbing force is removed. The ligament is strengthened 

 medially by blending with the deltoid ligament of the ankle-joint, and is supported 

 inferiorly by the tendon of the Tibialis posterior, which is spread out in a fan- 

 shaped insertion and prevents undue tension of the ligament or such an amount 

 of stretching as would permanently elongate it. The arch is further supported by 

 the plantar aponeurosis, by the small muscles in the sole of the foot, by the tendons 

 of the Tibialis anterior and posterior and Peronseus longus, and by the ligaments 

 of all the articulations involved. The lateral arch (see Fig. 291, page 277) is com- 

 posed of the calcaneus, the cuboid, and the fourth and fifth metatarsals. Its 

 summit is at the talocalcaneal articulation, and its chief joint is the calcaneocuboid, 

 which possesses a special mechanism for locking, and allows only a limited move- 

 ment. The most marked features of this arch are its solidity and its slight eleva- 

 tion; two strong ligaments, the long plantar and the plantar calcaneocuboid, 

 together with the Extensor tendons and the short muscles of the little toe, preserve 

 its integrity. 



While these medial and lateral arches may be readily demonstrated as the 

 component antero-posterior arches of the foot, yet the fundamental longitudinal 

 arch is contributed to by both, and consists of the calcaneus, cuboid, third cunei- 

 form, and third metatarsal : all the other bones of the foot may be removed without 

 destroying this arch. 



In addition to the longitudinal arches the foot presents a series of transverse 

 arches. At the posterior part of the metatarsus and the anterior part of the tarsus 

 the arches are complete, but in the middle of the tarsus they present more the 

 characters of half-domes the concavities of which are directed downward and 

 medialward, so that when the medial borders of the feet are placed in apposition 

 a complete tarsal dome is formed. The transverse arches are strengthened by the 

 interosseous, plantar, and dorsal ligaments, by the short muscles of the first and 

 fifth toes (especially the transverse head of the Adductor hallucis), and by the 

 Peronseus longus, whose tendon stretches across between the piers of the arches. 



BIBLIOGRAPHY. 



R. FICK: Handbuch der Anatomie und Mechanik der Gelenke (Bardeleben 's Handbuch der 

 Anatomie). 



