DISSECTION OF THE POSTERIOE LIMB. 81 



The Pehoneus (Plate 1 9). The tendon of this muscle emerges from the 

 thecal canal in the external lateral ligament of the tarsus, and joins the 

 tendon of the last-described muscle about the middle of the metatarsus. 



Action. — The same as the preceding muscle. 



The Superficial Flexor (flexor pedis perforatus) (Plate 19). The 

 tendon of this muscle, after playing over the os calcis, descends on the 

 middle line of the limb to the back of the fetlock, where it forms a 

 remarkable ring for the passage of the tendon of the deep flexor. Be- 

 yond this point the tendon bifurcates, and each half is inserted into the 

 upper extremity of the second phalanx, on its lateral aspect. In con- 

 nection with the tendon of this and the next muscle there is developed an 

 extensive synovial apparatus, termed the metatarso-phalangeal sheath, 

 which exactly resembles the metacarpo-phalangeal sheath of the fore 

 limb, described at page 34. 



Action. — It flexes successively the pastern and fetlock joints ; and, by 

 its insertion into the os calcis, it is also an extensor of the hock-joint. 

 It also mechanically maintains the hock in a state of extension as long 

 as the hip and stifle joints are kept extended by their proper muscles. 



The Deep Flexor (flexor perforans) (Plate 19). The tendon of 

 this muscle, after its passage through the tarsal sheath, descends 

 between the suspensory ligament and the superficial flexor. At the 

 fetlock it passes through the ring of the last-named muscle, descends 

 behind the digit, plays over the navicular bone, and finally becomes 

 inserted into the solar surface of the os pedis (see page 42). At the 

 upper part of the metatarsus it receives the check band, or subtarsal 

 ligament, which is analagous to the subcarpal ligament of the fore limb, 

 but not so strong. Like the analagous structure in the fore limb, it is 

 involved in sprain of the back tendons. A little lower the deep flexor is 

 joined on its outer side by the tendon of the flexor accessorius. 



Action. — It flexes successively from below upwards the interphalangeal 

 joints and the fetlock. 



Directions. — For the description of the foot, which is identical in the 

 fore and hind limbs, turn to page 35. If the student has already dis- 

 sected the foot in afore limb, he may proceed at once to the articulations. 



THE stifle-joint (pLATES 17 AND 18). 



This corresponds to the knee-joint of man. It comprises— (1) the articu- 

 lation between the patella and the femoral trochlea; and (2) the articula- 

 tion between the condyles of the femur and the proximal end of the tibia. 



Directions. — The various structures in connection with the joint are 

 to be examined in the order of the following description ; and in order 

 to expose them, the muscles, fat, etc., are to be removed from around 

 the joint, care being taken, in the first stage of the dissection, to pre- 

 serve the thin femoro-patellar capsule intact. 



