268 



OSTEOLOGY. 



III. UNGUA 



OR TERMINAL 

 PHALANX 



II. PHALANX 



configuration and in the arrangement of their articular facets they resemble 

 the phalanges of the fingers, though owing to the reduction in their size, the 

 bodies, particularly those of the second row, are often so compressed longitudin- 

 ally as to reduce the bone to a mere nodule. The 

 proximal end of each of the bones of the first row is pro- 

 portionately large, and is provided with a simple hollow in 

 which the head of the metatarsal bone rests; the distal 

 ends are furnished with condyloid surfaces. The proximal 

 extremities of the second row are each provided with two 

 small concavities, separated by a slight ridge, for articulation 

 with the condyles of the first row. The joint between the 

 second and third row displays the same arrangement the 

 third, or ungual phalanx, being easily distinguished by the 

 spatula-shaped surface at its extremity, on which the bed 

 of the nail is supported. 



The phalanges of the great toe, two in number, differ 

 from the others in their size and length. Into the base of 

 the first phalanx are inserted the short muscles of the great 

 toe, whilst the second phalanx receives on its plantar aspect 

 the insertion of the flexor hallucis longus muscle, the tendon 

 of the extensor hallucis longus being inserted into the 

 dorsal aspect. 



Ossification. Each phalanx is developed from two centres 

 OF ToEstpkTta? one primary for the body and distal extremity, the other for 

 Aspect). the epiphysis on the proximal end. The primary centres for the 



ungual phalanges are the first to appear, commencing to ossify 



from the eleventh to the twelfth week of foetal life. The centre for the ungual phalanx 

 of the great toe makes its appearance before that of its corresponding metatarsal bone. 

 The primary centres for the phalanges of the first row- appear from the fourteenth 

 to the sixteenth .week. The primary centres for the middle phalanges of the second and 



I. PHALANX 



METATARSAL 



i r 



FIG. 277. 



A. About the end of the third month. The primary centres of all the metatarsals are 

 shown as well as the centres for the phalanges of the great toe and the terminal 

 phalanx of the third toe. 



B. 1 A little later. The centres for the terminal phalanges of the medial four toes are 

 seen, as well as the centres for the first phalanges of the great and second toe. 



C. About the fourth month. The centres for all the terminal phalanges as well as 



those of the first row are well ossified. 



D. About the fifth month. In this the centre for the second phalanx of the second toe has 



already made its appearance. 



i This specimen displays the occurrence of anomalous centres within the tarsus the significance of 

 which is not apparent. The appearance is not due to any defect in the plate, but rectarred in repeated 

 radiographs. 



third toes begin to ossify about the sixth month, those for the fourth and fifth toes not 

 till later the body of the middle phalanx of the fourth toe being frequently cartilaginous 

 at birth, the normal condition in the case of the fifth toe (Lambertz). The proximal 

 epiphyses do not begin to ossify until about the fourth year, and are usually fused with 

 the diaphyses about the age of sixteen or eighteen. Union between the bodies and 

 epiphyses of the first row precedes that of the second and third rows. 



