90 OUTLINES OF EQUINE ANATOMY. 



it presents a small prominence roughened for attacliment 

 of tlie snpero-anterior annular ligament of the liock, 

 which runs obliquely downwards and outwards, over the 

 tendons of flexor metatarsi and extensor pedis towards the 

 infero- external part of the hone. The j^osterior surface 

 is divided into two parts. One superiorly placed, bounded 

 superiorly by the superior margin of the bone, internally 

 by the superior half of the inner margin, externally by a 

 line running from without inwards, obliquely downwards. 

 These enclose a triangular space to which popliteus is 

 attached. The rest of this surface is roughened by ridges 

 running obliquely inwards and downwards, to the outer 

 part of which is attached flexor pedis perforans to the 

 inner flexor pedis accessorius ; these two muscles are sepa- 

 rated by the posterior tibial artery, which runs through a 

 smooth groove, which at the inferior part of the superior 

 third of this surface presents the medullary foramen. The 

 inner margin of the bone is inferiorly unoccupied. Its 

 superior part affords attachment to popliteus and about the 

 centre of this half is a remarkable prominence serving to 

 mark out the course of the tendon of biceps rotator 

 tibialis. Superiorly this margin gives attachment to the 

 inner lateral ligament of the stifle joint. The oute^^ mar- 

 gin superiorly is roughened, affording attachment to the 

 outer lateral ligament ; below this is a roughened line to 

 which the upj^er extremity of the fibula is attached by 

 white fibrous tissue ; below this a smooth surface helping 

 to form the fibular arch through which the anterior tibial 

 vessels pass. This margin as far down as the inferior 

 extremity gives attachment to the white fibrous tissue 

 which connects it to the fibula. Its superior part is sepa- 

 rated from the anterior ridge of the bone by a deep smooth 

 rounded groove, in which lies a bursa for passage of the 

 tendon common to flexor metatarsi and extensor pedis. 

 Flexor pedis perforans extends as far up as the posterior 

 2:)art of the expanded superior extremity of this margin. 



The superior surface of the bone is divided into two 

 articular surfaces by a spine which runs from behind for- 

 wards, presenting an irregular groove extending from the 

 perforated line which separates the anterior ridges from 

 this superior surface, to the posterior margin. It is rough 

 and prominent, anteriorly affording attachment to one of 

 the crucial ligaments, and to the anterior ligaments of the 



