168 SKELETON OF THE DOG 



The fibula extends the entire length of the region. It is slender, somewhat 

 twisted, and enlarged at either end. The upper part of the shaft is separated from 

 the tibia by a considerable interosseous space, but the lower part is flattened and 

 closely applied to the tibia. The proximal end is flattened and articulates with 

 the external condyle of the tibia. The distal end is somewhat thicker and forms 

 the external malleolus. It articulates internally with the tibia and the tibial tarsal 

 bone. Externally it bears two tubercles. 



The patella is long and narrow. The anterior surface is convex in both direc- 

 tions. The articular surface is convex from side to side and slightly concave from 

 above downward. 



The tarsus comprises seven bones. The tibial tarsal consists of a body, neck, 

 and head, like the bone in man. The body presents a trochlea above for articula- 

 tion with the tibia and fibula. The posterior surface has three facets for articulation 

 with the fibular tarsal bone. The head is directed a little inward and articulates 

 with the central. The fibular tarsal has a long anterior process or "beak," but 

 the inner process (sustentaculum) is short. The tuber calcis is grooved from 

 before backward. The central has a concave proximal surface adapted to the head 

 of the tibial tarsal. Its distal surface articulates with the first, second, and third 

 tarsals. It bears two tubercles posteriorly. The first tarsal is flattened and ir- 

 regularly quadrangular; it articulates above with the central and below with the 

 first metatarsal. The second tarsal is the smallest and is wedge-shaped; it articu- 

 lates below with the second metatarsal bone. The third tarsal is also wedge- 

 shaped, the base being in front; it articulates with the third metatarsal below. 

 The fourth tarsal is remarkably high, and resembles a quadrangular prism; it 

 articulates with the fibular tarsal above, the fourth and fifth metatarsal below, and 

 the central and third tarsal bones internally. A groove for the tendon of the pero- 

 neus longus crosses its outer and posterior surface, and above it are one or two 

 tubercles. 



Five metatarsal bones are present. The first is commonly very small and has 

 the form of a blunt cone, somewhat compressed laterally. It articulates with the 

 first tarsal and furnishes insertion to the tibialis anterior muscle. In some cases 

 it fuses with the first tarsal; when the first digit is well developed, its metatarsal 

 may resemble the others (except in size) or be reduced in its proximal part to a 

 fibrous band. The other metatarsals are a little longer than the corresponding 

 metacarpals. Their proximal ends are elongated from before backward and have 

 posterior projections, which in the case of the third and fourth usually bear facets 

 for articulation with two small rounded sesamoid bones. In other respects they 

 resemble the metacarpals. 



The first digit is often absent. When present, its development varies and it 

 contains one or two phalanges. In other cases the digit is double. The phalanges 

 of the other digits resemble those of the fore limb. 



