OSTEOLOGY OF THE HORSE. 63 



leg bones, become of this quadruped the basis of the part we 

 are in the habit of calling the thigh. 



TIBIA. 



Situation — Between the stifle and the hock. 



Form — Long, straight, prismatic: larger superiorly than infe- 

 riorly. 



Direction — Oblique; but contrariwise to the round bone. 



Division — Into body, superior and inferior extremities. 



The body exhibits three faces and three angles. Ttvo of the 

 faces are smooth, and are seen anteriorly ; one looking outwards, 

 the other inwards: the former covered by the extensor pedis, the 

 latter by the skin. The posterior face is the broadest, and is 

 strongly marked with several longitudinal muscular furrows. 

 'The anterior angle is rounded ofi", and below disappears altoge- 

 ther : the sides are sharpened and roughened by muscular attach- 

 ment. 



The superior extremity, more bulky and extensive than 

 the inferior, exhibits — Superiorly, two irregularly ovoid flattened 

 articulatory surfaces, which, by means of intervening cartilages, 

 are accommodated to the condyles of the round bone : these are 

 parted by a small sharp elevation and two asperous pits, into 

 which latter are fixed the crucial ligan)ents. Anteriorly, a jutting 

 pyramidal tuberosity, from which a rough ridge runs downward 

 into the anterior angle of the body, while, above, it ends in a blunt 

 asperous point, turned outwards. At the sides are the two lateral 

 processes, the external the more projecting, for the lateral liga- 

 ments. Between the external lateral process and the tuberosity, 

 is a groove for the passage of the tendon of the extensor pedis ; 

 and below this groove a broad excavated portion of surface, 

 from which arises the flexor metatarsi. The external condyle has 

 on its side a small transversely oval excavation, marking the 

 place of junction of the fibula. 



The inferior extremity, flattened and spreading but 

 little wider than the body itself, consists of two deep articular 

 grooves, running obliquely from before backwards, and from with- 

 out inwards, and of three sharpened projections : — one, extended 

 obliquely, forms the partition between the grooves ; the others 

 form the lateral processes, of which the internal is more promi- 

 nent than the external, both being roughened exteriorly for the 

 lateral ligaments. The external lateral process has a groove on 

 its side, for the passage of the tendon of the peroneus. 



Connexion. — With the round bone, above ; the os calcis, below. 



Development. — The extremities, originally epiphyses, become 

 apophoses prior to the adult period. 



