102 THE SONES. 



bone, the tibial arch. Its superior extremity, wide and flattened on both 

 sides, has received the name of head; it offers, on its internal face, a 

 diarthrodial facet to articulate with the external and superior tuberosity 

 of the tibia ; on its external face it shows ligamentous imprints. The . 

 inferior extremity of the fibula terminates in a blunt point, and gives 

 attachment to the ligamentous fibres that unite it to the tibia. 



The fibula is sometimes continued to the external inferior tuberosity 

 of the latter bone, with which it is confounded ; and as it is particularly 

 under such circumstances that this tuberosity has been noticed to be deve- 

 loped from a special nucleus, it seems quite natural, having regard to 

 the disposition observed in pachyderms and carnivores, to consider it as 

 the inferior extremity of the fibula joined to the tibia. "With these animals, 

 indeed, the tuberosity or external malleolus is formed by the inferior ex- 

 tremity of the fibula. 



Structure and development. — This bone is very compact, and developed 

 from a single nucleus of ossification. 



3. Patella. 



A small, short, and very compact bone, situated in front of the femoral 

 trochlea, and annexed to the tibia, to which it is attached by three extremely 

 solid ligamentous bands. 



The small polyhedron which it represents only offers for observation 

 three faces : the superior, roughened, and serving for the insertion of the 

 triceps cruralis and rectus muscles ; the anterior, convex and irregular ; and 

 the third, the posterior, moulded on the femoral trochlea, to which it is but 

 imperfectly adapted. In the fresh state, however, the articular surface 

 formed by the latter face is completed by a fibro-cartilaginous apparatus, 

 which will be noticed when describing the femoro-tibial articulation. This 

 articular surface is composed : 1, Of a median ridge, which occupies the 

 bottom of the trochlear cavity ; 2, Of two depressed, gliding, lateral facets 

 on the sides of this cavity; the internal facet is always larger than the 

 external, a disposition which permits the patella of one limb to be distin- 

 guished from that of the other. 



POSTERIOR FOOT. 



This region, which bears the greatest resemblance to the same region in 

 the anterior limb, comprises three subdivisions : the tarsus, metatarsus, 

 and the digital region. 



1. Bones of the Tarsus. 



These are short, very compact bones, six or seven in number, and 

 situated between the inferior extremity of the tibia and the superior 

 extremity of the metatarsal bones ; they are arranged, like the bones of 

 the carpus, in two tiers — a superior and an inferior. 



The su])erior row only comprises two bones, the largest ; these are the 

 astragalus and the calcaneus (or calcis). The inferior row is formed, out- 

 wardly, by the cuboides alone ; inwardly and anteriorly, it is subdivided 

 int) two secondary rows, the superior of which is constituted by the 

 scaphoides, and the inferior by the large and small cuneiform boues. The 

 last is sometimes divided into two, in which case there are three cuneiforms ; 

 then the total number of the bones is seven. 



Astragalus.— An irregular cubical bone, situated in front of the 



