The =metatarsal= bones (Ossa metatarsalia), three in number, have the
same general arrangement as the metacarpal bones, but present some
important differences. Their direction is slightly oblique, downward and
a little forward.
The =large= or =third metatarsal= bone is about one-sixth longer than
the corresponding metacarpal; in an animal of medium size the difference
is about two inches. The shaft is more cylindrical, and is almost
circular on cross-section, except in its lower part. At the upper part
of its external surface there is a groove, which is directed obliquely
downward and backward, and is continued by the furrow formed by the
apposition of the external metatarsal bone; it indicates the course of
the great metatarsal artery. A faint impression in a similar place on
the inner side marks the position of the corresponding vein. The
nutrient foramen is relatively higher than on the metacarpal bone. The
proximal extremity is much wider from before backward than that of the
metacarpal bone. Its articular surface is slightly concave, and is
marked by a large central non-articular depression, continued outward by
a deep notch. The greater part of the surface articulates with the third
tarsal, but there is an outer facet for the fourth, and usually a small
facet posterointernally for the second tarsal bone. Posteriorly there
are two pairs of facets for articulation with the small metatarsal
bones. The front is crossed by a rough ridge for insertion, which
becomes larger and turns downward on the outer side behind the vascular
groove. The distal extremity closely resembles that of the corresponding
metacarpal bone.
In some cases the lower part of the shaft is bent backward somewhat.
The articular surface extends a little higher behind than in the case
of the metacarpal bone. The large metatarsal bone is even more
strongly constructed than the metacarpal. The shell of compact
substance is very thick in the middle of the shaft, especially in
front and internally.
The =small metatarsal= bones are a little longer than the corresponding
metacarpals. The =external= (fourth) =metatarsal= is relatively massive,
especially in its upper part. The head is large and outstanding, and
bears two facets above for the fourth tarsal, and two in front and
internally for articulation with the large metatarsal; elsewhere it is
roughened for attachment. The =internal= (second) =metatarsal= is much
more slender than the outer one, especially in its upper part. The head
bears two facets above for the first and second tarsals, and sometimes
one for the third tarsal.