THE STIFLE JOINT 



195 



about half an inch. It pouches upward under the quadriceps femoris for a distance 

 of two or three inches, a pad of fat separating the capsule from the muscle. 

 Below the patella it is separated from the straight ligaments by a thick pad of 

 fat, but inferiorly it is in contact with the femoro-patellar capsules. The joint 

 cavity is the most extensive in the body. It usually communicates with the 

 inner femoro-tibial joint cavity by a slit-like opening situated at the lowest part 

 of the inner ridge of the trochlea. A similar, but smaller, communication with the 

 outer femoro-patellar capsule is often found at the lowest part of the outer ridge. 



The inner communication appears to be constant in adult horses, but is nal)le to be over- 

 looked on account of the fact that it is covered by a valvular fold of the synovial membrane. It 

 is about half an inch wide, and lies under the narrow articular area which connects the trochlea 

 and internal condyle. The outer communication occiu's in IS to 2.") per cent, of cases, according 

 to Baum. It is instructive to distend this capsule and thus obtain an idea of its potential capa- 

 city and relations (Fig. 156). 



Accessory cartilage of patella 

 Internal ridge of trochlea of femur 



Middle patellar ligament >■■ 



Internal semilunar cartilage -f-^ 



Internal patellar ligament f"?'iRr j( 



Tuberosity of tibia 



External fcmoro-patdlar ligament 



External patellar ligament 



External fe?noro-tibial ligament 

 External semilunar cartilage 



External condyle of tibia 



- Fibula 



Fig. 157. — Left Stifle Joint of Horse, Front View, in Extension. 

 The capsules are removed. IS, Femur; 20, patella; 21, tibia. (After Ellenberger-Baum, Anat. fiir Kvinstler.) 



Ligaments. — The lateral femoro-patellar ligaments, external and internal 

 (Ligamentum femoro-patellare fibulare, tibiale) , are two thin bands which reinforce 

 the capsule on either side. The external ligament is fairly distinct; it arises from 

 the external epicondyle of the femur just above the lateral femoro-tibial ligament, 

 and ends on the external border of the patella. The internal ligament is thinner 

 and is not distinct from the capsule; it arises above the internal epicondyle, and 

 ends on the patellar fibro-cartilage. 



The patellar ligaments (Ligamenta patellae), also called the straight ligaments 

 of the patella, are three very strong bands which attach the patella to the tuberosity 

 of the tibia. The external patellar ligament is attached above to the outer part 

 of the anterior surface of the patella, and below to the outer part of the tuberosity. 

 It receives a strong tendon from the biceps femoris muscle. The middle patellar 

 ligament extends from the front of the apex of the patella to the lower part of 



