764 MAMMALIAN ANATOMY 



base, and extends distally, forming the hook proper. Both surfaces 

 are concave, especially near the middle, and rough for ligamentous 

 attachment. The principal difference between the two surfaces lies 

 in the formation of the region near the distal border. 



On the tibial surface (Fig. 581) there are two prominent distal 

 swellings, one dorsal and one plantar, separated by a deep groove 

 which produces the decided emargination on the tibial side of the 

 distal surface. These swellings are smooth, and articulate with cor- 

 responding depressions on the fibular side of the base of the second 



metatarsal bone. 



FIG. 581. 



Dorsal Side. 



With Cuboid. 



Distal Side. ? A Proximal Side. 



For Tendon of 



PERONEUS LONGUS. 



Plantar Side. 



LEFT ECTOCUNEIFORM, FIBULAR SURFACE. 



On the fibular surface only the upper of these swellings is present, 

 and it is not so prominent ; it articulates with a facet on the dorso- 

 distal angle of the tibial surface of the cuboid. There runs along the 

 proximal margin on each surface an elongated vertical facet ; it is 

 more distinctly marked on the fibular than on the tibial surface. On 

 the fibular side it articulates with a long facet in the middle of the 

 tibial surface of the cuboid ; on the tibial side it articulates with the 

 fibular side of the mesocuneiform. As stated above, each lateral sur- 

 face is continued downward into the narrower lateral surface of the 

 plantar hook. 



Nomenclature. Ectocuneiform is from the Greek ecto, without, 

 and the Latin cuneiform, wedge-shaped. External cuneiform, os cunei- 

 forme tertium, and tarsale III. are also used. The German equivalent 

 is das dritte or aussere Keilbein, the French le troisieme cuneiforme. 



Determination. The ectocuneiform is known by its hook. When 

 the dorsal surface is held uppermost and the T-shaped distal surface 

 toward the student, the smaller deeper excavation on the fibular side 

 of the latter surface is on the side to which the bone belongs. 



