282 OUTLINES OF EQUINE ANATOMY. 



sions of perforatus, wliich become attaclied to tlie extre- 

 mities of this ridge inclined to the lateral surfaces of the 

 bone. Between this ridge and the inferior articulatory 

 surface the posterior part of the bone is unoccupied, merely 

 presenting foramina for the passage of vessels into the 

 bone. The lateral surfaces are exactly similar. Superiorly 

 they are roughened for attachment of the broad lateral 

 ligament of the pastern-joint. Inferiorly, inclined to the 

 anterior surface, is a peculiar depression, which, with its 

 fellow, seems as though the bone, when in a soft state, had 

 been compressed between the thumb and finger. To this 

 the lateral ligament of the pedal joint runs. The anterior 

 surface of this bone is occupied by the expanded inferior 

 part of extensor pedis tendon, which is attached somewhat 

 firmly by areolar tissue. 



OS PEDIS is an irregular bone, and since it receives no 

 bony support from below is a floating bone. It is sym- 

 metrical, presenting two very similar halves, the inner of 

 which is the smallest. At the extreme antero- inferior part 

 may bo seen in many cases a notch, a trace of the division, 

 such as we see in ruminants, of this bone into two similar 

 parts. It presents three surfaces : supero-posterior, infero- 

 posterior, and antero-lateral. The supero-posterior surface 

 centrally is articulatory, presentmg a surface covered with 

 cartilage, divided primarily into two parts. The anterior 

 part is roughly heart-shaped, concave in an antero-posterior 

 direction, elongated and slightly convex from side to side. 

 Anteriorly it terminates in an obtuse point, extending in 

 an upward direction on the posterior surface of the coronal 

 process ; posteriorly it presents an oblique angled indenta- 

 tion, into which the posterior part fits. The sides of the 

 oblique angle meet the external convex margins of the 

 articulatory surface at an acute angle outwardly and pos- 

 teriorly. This surface centrally presents an antero-poste- 

 rior broad ridge with a shallow concavity on either side, 

 the inner being slightly the largest. It articulates ante- 

 riorly with OS coronse, and this portion is directly continuous 

 with that between its posterior margins, with which os 

 naviculare comes in apposition, and which is bounded pos- 

 teriorly by a line extending from one posterior angle of the 

 heart-shaped surface to the other. This surface of the 

 bone is completed by a roughened ridge on each side run- 

 ning at first outwards and then directly backwards for 



