100 THE SKELETON OF THE HORSE 



The internal epicondyle (Epicondylus medialis) is a rounded prominence on 

 the internal surface of the internal condyle, to which the internal lateral ligament 

 and the adductor muscle are attached. The corresponding external epicondyle 

 (Epicondylus lateralis) is less distinct; it presents a mark where the lateral liga- 

 ment is attached, below and behind which there is a depression (Fossa musculi 

 poplitei) in which the popliteus muscle arises. Between the external condyle and 

 trochlea is the extensor fossa (Fossa extensoria), in which the tendon of origin of 

 the anterior extensor and peroneus tertius is attached. 



Development. — The shaft and the distal end each ossify from one center, but 

 the proximal end has two centers, one of which is for the great trochanter. The 

 edge of the external trochanter also has a separate center. The proximal end fuses 

 with the shaft at three to three and a half years, the distal at about three and a 

 half years. 



f inner ridge 

 Trochlea \ 



[ outer rii 



Extensor fossa -- 



External epicondyle-- 



Depression for origin of_ 

 popliteus 



- Internal epicondyle 



External condyle ^-^^^^m \ ^^^^g- Internal condyle 



^^^^^^^^^ ^^^^^^^^^^ 



Inter condyloid fossa 



Fig. 67. — Distal Extremity^f Right Femur of Horse, End View. 



THE TIBIA 



The tibia is a long bone which extends obliquely downward and backward 

 from the stifle to the hock. It articulates above with the femur, Ijelow with the 

 tarsus, and externally with the fibula. It possesses a shaft and two extremities. 



The shaft or body (Corpus tibiae), large and three-sided above, becomes smaller 

 and flattened in the sagittal direction below, but widens a little at the distal end. 

 It pres(nits for notice three surfaces and three borders. The internal surface 

 (Facies medialis) is broad above, where it furnishes insertion to the internal lateral 

 ligament and the sartorius and gracilis muscles; below this it is convex and sub- 

 cutaneous. The external surface (Facies lateralis) is smooth and somewhat spiral. 

 It is wide and concave in its upper part, below which it becomes narrower and 

 sliglitly convex, and winds gradually to the front of th(^ lione; near the distal end 

 it widens a little, becomes fiat, and faces forward. The posterior surface (Facies 

 posterior) is flattened, and is divided into two parts by the rough popliteal line, 

 which runs obliquely from the upper part of the external border to the middU^ of 

 the internal border. The triangular area above the line is occupied by the popliteus 

 muscle, while the area below is marked l)y rough lines (Linese musculares) to which 

 the deep flexor muscle of \\\v digit is attached ; the lines fade out l)elow, where the 

 surface is smooth and flat. The nutrient foramen is situated on or near the 

 popliteal line. The anterior border is very prominent in its upper third, forming 

 the tibial crest (Crista tibiae); below it js reduced to a rough line, which ends at a 



