THE SKELETON. 7! 
tebrates is similar to that of the carpus. Three bones, a 
tibiale, intermedium, and fibulare, compose the proximal 
row, while five tarsalia form the distal row. The centrale 
occupies the center of the tarsal region. In the adult mam- 
mal, fusion of some of these elements occurs, so that not 
more than seven distinct bones are present in any form. 
The astragalus contains the tibiale and intermedium, while 
the fourth and fifth tarsalia form the cuboid. 
The metatarsus consists of five bones, the first of which 
is rudimentary, while the other four are longer than the 
metacarpus, which they resemble (Fig. 43). The first meta- 
tarsal is smaller than any bone of the tarsus. It articulates 
with the internal cuneiform and is also in contact with the 
second metatarsal. The four long metatarsals have a slight 
dorsal convexity, each one consisting of a base or enlarged 
proximal part, a shaft or middle portion, and a head or 
distal rounded articular process. On the plantar surface of 
the head of each metatarsal is a median spine, on each side 
of which is a concavity for a sesamoid bone. These sesa- 
moid bones are frequently lost in cleaning the skeleton. 
The number of functional metatarsals in mammals varies 
from one to five. Usually the number of metacarpals and 
metatarsals is the same, but in the tapir there are four meta- 
carpals and but three metatarsals. All Monotremata, Car- 
nivora, and Primates have five metatarsals, but in the cats, 
dogs, and hyenas the first metatarsal is vestigial. In early 
geological times all mammals possessed five metatarsals, the 
number of which in many cases has gradually diminished 
owing to environment, as is shown in the phylogeny of the 
horse (Fig. 35). 
The Equidz possess but one functional metatarsal and 
two rudimentary ones, although Orohippus, the ancestor of 
the horse, had three functional metatarsals. 
The phalanges of the cat’s foot are twelve in number. 
