272 



A MANUAL OF ANATOMY 



the fourth toe gives partial insertion internally to the second plantar inter- 

 osseous, and externally to the fourth dorsal interosseous. The base of the 

 first phalanx of the fifth toe gives partial insertion internally to the third 

 plantar interosseous, and externally insertion to the abductor minimi digiti 

 and flexor brevis minimi digiti. The second and ungual phalanges of each 

 of the four outer toes give insertion to extensor and flexor tendons, as in the 

 case of the corresponding bones of the four inner fingers. 



The medullary foramen and the canal to which it leads are, 

 in each phalanx, directed towards the distal end. The nutrient 

 arteries are derived from the corresponding plantar digital arteries. 



Structure. — The structure of each phalanx resembles that of the 

 corresponding bone in the hand. 



Varieties. — Ankylosis of the ungual and second phalanges of the fifth toe 

 is of frequent occurrence, and may even involve those of other toes, up to and 

 including the second. 



Sesamoid Bones. — These are two in number, and are of large size. 

 They are associated with the two heads of insertion of the flexor 

 brevis hallucis, and lie on the plantar aspect of the head of the first 

 metatarsal bone. 



Appears in the loth Year, 

 and joins at i6 



Appears at 6th Month ,J 

 (intra-uterine) 



gth Month (intra-uterine) 

 I St Year 



7th Month 

 (intra-uterine). 



4th Year 

 4th Year 



3rd Year 



Appears between 4th and 8th Year 

 and joins about 19 



gth Week (intra-uterine) 



Appears between 4th and 8th Year 

 and joins about 19 

 Same as for Metatarsals 



:} 



Epiphysis 

 Primary Centre 



Fig. 164. — Ossification of the Bones of the Foot. 



Ossification of Metatarsal Bones and Phalanges. — Each bone ossifies in 

 cartilage from one primary, and one secondary, centre, which closely agree with 

 those of the corresponding bones of the hand in their disposition. The primary 

 centres for the shafts appear about the ninth week of intra-uterine life, 

 whilst the secondary centres appear between the fourth and eighth year. Each 

 epiphysis joins its shaft about the nineteenth year. 



