PLEXOR TENDONS AND SUSPENSORY LIGAMENT. 



831 



of two parts continuous with each other ; a parietal, lining the aponeurosis 

 or other supporting tissue, and a visceral, investing the proper covering 

 of the tendon. The opposed surfaces are lined with endothelium. The 

 carpo-metacarpal sheath, extending from ahout two inches above the carpus 

 to near the middle of the cannon, 

 lines the carpal arch, and part of the 

 metacarpal aponeurosis, and is reflected 

 on both tendons in the carpal ai-ch 

 and below on perforans, posterior sur- 

 face of subcarpal ligament and anterior 

 surface of perforatus tendon. From an 

 inch or two below the carpal arch to 

 the upper margin of the sesamoid 

 sheath the perforatus has no synovial 

 on its posterior surface, and the an- 

 terior surface of this portion of the 

 tendon is separated by loose connective 

 tissue from the parietal synovial of 

 the perforans. 



The great sesamoid sheath extends 

 from the level of the " buttons " to 

 the middle of the os coronse, where it 

 is separated from the navicular bursa 

 by an attachment of the perforans. 

 It lines the aponeurosis and sesamoid 

 pulley and is reflected on flexor ten- 

 dons, being modified at the sesamoids 

 by the absence of endothelium on the 

 anterior surface of the perforans. 

 There is no synovial covering on the 

 portion of the posterior surface of 

 the perforatus which is united to the 

 aponeurosis of the fetlock. 



The navicular bursa or sheath ex- 

 tends from middle of os coronse to 

 below the navicular bone ; it forms 

 a short synovial sac between the 

 perforans and the navicular bone and 

 its interosseous ligament. 



Tendon is made up of groups of 

 parallel white fibrils, interspersed with 

 flattened nucleated connective tissue 

 cells, arranged in rows running in the 

 direction of the tendon fibres. Be- 

 tween the bundles are interfascicular 

 spaces, and primary and secondary 

 connective tissue septa, continuous 



with the peritendinous covering. The nerves (few and non-medullated), 

 blood-vessels, and lymphatics ramify in the septa. The subcarpal and 

 subtarsal ligaments have thicker interfascicular septa and are more 

 vascular than the tendons. 



Rupture of the flexor tendons is produced by external violence, 



Fig. 475. — Showing relative positions 

 of tendons, &c., in the metacarpal 

 region. Immediately behind the 

 metacarpus lies the suspensory or 

 superior sesamoid ligament ; the 

 short band extending from behind 

 the knee half-way down the meta- 

 carpus is the check ligament ; behind 

 it lies the perforans tendon, to which 

 it is connected ; the hindmost of the 

 tendons shown is that of the flexor 

 pedis perforatus muscle. 



