200 THE ARTICULATIONS OF THE HORSE 



arthrodia, which have joint surfaces and ligaments of such a nature as to allow 

 only a minimal amount of gliding motion. 



As in the case of the carpal joints, it is convenient to describe first the common 

 capsule and ligaments, which are the more important practically, and then to 

 consider very briefly the special ligaments. 



The fibrous part of the joint capsule is attached around the margin of the 

 tibial articular surface above and the metatarsal surfaces below; it is also attached 

 in part to the free surface of the bones which it covers, and blends with the lateral 

 ligaments. Its anterior part (anterior ligament) is rather thin; in distention of the 

 capsule, as in "bog-spavin," its antero-internal part, which is not bound down by 

 the tendons passing over the joint, forms a fluctuating swelling over the inner ridge 

 of the trochlea. The posterior part (posterior and tarso-metatarsal ligaments) is 

 very thick, and is intimately attached to the tarsal bones. Its superficial face is 

 in part cartilaginous, and forms a smooth surface for the perforans tendon. Su- 

 periorly, it pouches upward behind the distal end of the tibia for a distance of about 



Short internal lateral ligament ^-i|r ^^?**»* 



Long internal lateral ligament -\ ^ l^»^-lJ "^~0 



JsMKkjS ,'-') External lateral ligament 



Internal small metatarsal hone 



External small metatarsal hone 



Fir,. 164. — Left Hock Joint of Horse, Anterior View. 

 21, Tibia; 22, trochlea of tibial tarsal bone; 25, large metatarsal bone; 50, dorsal or oblique ligament. (After 



Ellenberger-Baum, Anat. fiir Kiinstler.) 



two inches (ca. 5 cm.). Inferiorly, it is continued downward, forming the sub- 

 tarsal or check ligament, which unites with the perforans tendon about the middle 

 of the metatarsus. 



There are four synovial sacs: 1. The tibio-tarsal sac lubricates the proximal 

 joint, and is much the largest and most important. It is chiefly involved in the 

 swelling produced by excess of fluid in the joint cavity, when the capsule liulges 

 antero-internally and postero-superiorly. 2. The first intertarsal sac lines the joints 

 formed by the tibial and fibular tarsal bones above, and the central and fourth 

 tarsals below; it commimicates in front with the proximal synovial capsule. 3. 

 The second intertarsal sac lubricates the joints formed between the central tarsal 

 and the l)ones below and on either side. 4. The tarso-metatarsal sac lubricates 

 the joints formed between the tarsal and metatarsal bones, those between the 

 proximal ends of the metatarsal bones, and those formed by the third tarsal with 

 the bones on either side. 



Common Ligaments. — The external lateral ligament (Ligamentum collaterale 



