THE PHALANGES 



203 



The fourth metatarsal (fig. 248), smaller in size than the preceding, is distinguished by 

 the quadrilateral facet on the base, for the cuboid. The medial side presents a large facet 

 divided by a ridge into an anterior portion for articulation with the third metatarsal and a 

 posterior portion for the third cuneiform. Occasionally the cuneiform part of the facet is 

 wanting. On the lateral side of the base is a single facet for articulation with the fifth 

 metatarsal. 



The fifth metatarsal (fig. 249), is shorter than the fourth, but longer than the first. It is 

 recognised by the large nipple-shaped process, known as the tuberosity, which projects on the 

 lateral side of the base. It constitutes the hindmost part of the bone and gives insertion to 

 the peroneus brevis on the dorsal aspect, and flexor brevis digiti quinti and the occasional 

 abductor ossis metatarsi quinti on the plantar aspect. The fifth metatarsal articulates behind 

 by an obliquely directed triangular facet with the cuboid, and on the medial side with the 

 fourth metatarsal. The plantar aspect of the base is marked by a shallow groove which 

 lodges the tendon of the abdtictor digiti quinti, and the dorsal surface, continuous with the 

 superior surface of the shaft, receives the insertion of the peroneus tertius. The head is small 

 and turned somewhat laterally in consequence of the curvature of the shaft in the same 

 direction. The shaft differs from that of any of the other metatarsals in being compressed 

 from above downward, instead of from side to side, so as to present superior, inferior, and 

 medial surfaces. It gives origin to the lateral head of the fourth dorsal interosseous and the 

 third plantar interosseous muscles. The nutrient foramen is situated on its tibial side and is 

 directed toward the base. 



Ossification. — Each metatarsal ossifies from two centres. The primary nucleus for the 

 shaft appears in the eighth week of embryonic life in the middle of the cartilaginous metatarsal. 

 At birth, each extremity is represented by cartilage, and that at the proximal end is ossified by 

 extension from the primary nucleus, except in the case of the first metatarsal. For this, a 

 nucleus appears in the third year. 



The distal ends of the four lateral metatarsals are ossified by secondary nuclei which make 

 their appearance about the third year. Very frequently an epiphysis is found at the distal end 

 of the first metatarsal as well as at its base. The shafts and epiphyses consolidate at the twen- 

 tieth year. The sesamoids belonging to the flexor hallucis brevis begin to ossify about the fifth 

 year. 



THE PHALANGES 



The phalanges (fig. 250) are the bones of the toes, and number in all fourteen. 

 Except the great toe, each consists of three phalanges, distinguished as first 

 (proximal), second and third (distal) ; in the great toe the second phalanx is absent. 



Fig. 250. — The Phalaxges op the Middle Toe. 



Second 

 phalanx 



There is thus a similarity as regards number and general arrangement with the 

 phalanges of the fingers. With the exception of the phalanges of the great toe, 

 which are larger than those of the thumb, the bones of the toes are smaller and 

 more rudimentary than the corresponding bones of the fingers. In all the pha- 

 langes, the nutrient foramen is directed toward the distal extremity. 



The phalanges of the first row are constricted in the middle and expanded at either ex- 

 tremity. The shaft.s are narrow and laterally compressed, rounded on the dorsal and concave 



