204 



THE SKELETON 



on the plantar aspects. The base of each presents a single oval concave facet for the convex 

 head of the corresponding metatarsal, whilst the head forms a pulley-like surface [trochlea 

 phalangis], grooved in the centre and elevated on each side for the second phalanx. 



The phalanges of the second row are stunted, insignificant bones. Their shafts, besides 

 being much shorter, are flatter than those of the first row. The bases have two depressions, 

 separated by a vertical ridge, and the heads present trochlear surfaces for the ungual phalanges. 



The third, or ungual phalanges are easily recognised. The bases articulate with the second 

 phalanges; the shafts are expanded, forming the ungual tuberosities which support the nails, 

 and their plantar surfaces are rough where they come into relation with the pulp of the digits. 



The muscles attached to the various phalanges may be tabulated thus: — 



The first phalanx of the hallux gives insertion to the flexor hallucis brevis; abductor hallucis; 

 adductor haUucis transversus and obliquus; extensor digitorum brevis. 



The first phalanx of second toe : The first and second dorsal interosseous. 



The first phalanx of third toe : Third dorsal interosseous; first plantar interosseous. 



The first phalanx of fourth toe : Second plantar interosseous; fourth dorsal interosseous. 



The first phalanx of fifth toe: Third plantar interosseous; flexor digiti quinti brevis; and 

 abductor digiti quinti. 



The terminal phalanx of hallux: Flexor hallucis longus; extensor hallucis longus. 



Fig. 251. — A Longitudinal Section of the Bones of the Lower Limb at Birth. 



The centre for the lower extremity of 

 the femur appears early in the 

 ninth month 



The centre for the upper end of the 

 tibia appears about a week before 

 birth 



Cartilage for the patella appears about 

 the fourth month of intra-uterine 

 life 



The centre for the talus appears in 

 the seventh month 



The centre for the calcaneus appears 

 in the sixth month 



[;/ The centre for the navicular appears in the fourth year 

 For the first cuneiform appears in the third year 



First phalanx of hallux 



Second phalanx of hallux 



The second phalanges of the remaining toes : Dorsal expansion of the extensor tendons, 

 including extensor digitorum longus, extensor digitorum brevis (except in the case of the fifth 

 toe), and expansions from the interossei and lumbricales. 



TJie third phalanges: Flexor digitorum longus; dorsal expansion of the extensor tendon 

 with tlif! associiitod niusclcs. 



Ossification. — Like the corresponding bones of the fingers, the phalanges of the toes ossify 

 from a primary and a secondary nucleus. In each, the centre for the shaft ajipears during the 

 eighth or ninth week of embryonic life. The secondary centre forms a scale-like epi])hysis for 

 the proximal end between the fourth and eighth years, and union takes place in the eighteenth 

 or nineteenth year — i. e., earlier than t he corresponding epiphyses in the fingers. The primary 

 centres for the third phalanges appear at the distal extremities of the bones. 



Sesamoid Bones 



In the foot a pair of sesamoid bones is constant over the mctatarso-phalangcal joint of the 

 great toe in the tendons of the flexor hallucis brevis. One sometimes occurs over the inter- 

 phalangeal joint of the same toe and over the metatarso-phalangeal joints of the second and 

 fifth and rarely of the third and fourth toes. 



