OF DIDELPIIYS VIRGINIANA. 127 



joint — -just above the insertion of the gracilis. The fleshy part suddenly contracts into a 

 narrow, flat tendon, about an inch long. The muscle lies at first along the lower border of 

 the biceps; and afterwards crosses the semimembranosus diagonally. Near the middle of 

 its course there is a slight contraction, produced by a partial tendinous intersection ; the 

 cruro-coccygeus here effects the remarkable inosculation about to be described. In general 

 characters this muscle most resembles the semimembranosus of anthropotomy. 



Cruro-coccygeus. — (Fig. 32, i, i', fig. 31, n.) This singular muscle arises from the trans- 

 verse process of the third coccygeal vertebra, by a distinctly marked, short, narrow, flat 

 tendon, and runs, as a flattened fleshy band of moderate size, directly transverse, past the 

 tuberosity of the ischium, along the posterior border of the semitendinosus, with which it 

 is in close apposition. It represents the posterior border of the thigh. At the constriction 

 of the semitendinosus just mentioned, it dips into the substance of the latter, and the fleshy 

 fibres of the two are completely blended. Separating again almost immediately after this 

 inosculation, the muscle divides into two slips that diverge from each other, one proceed- 

 ing to the inner, the other to the outer, side of the leg. The outer fasciculus, on reaching 

 the leg, ends in a broad, thin aponeurosis, directly continuous with the aponeurotic tendon 

 of the biceps, and is lost in the general fascia of the leg. The inner slip proceeds to be 

 inserted near the tendon of the semitendinosus into the shaft of the tibia. Acting from 

 the tail, this muscle is a flexor of the leg and extensor of the thigh ; the occasion for its 

 presence may be found in the necessity for an aid to, and increase of the power of the 

 other muscles of the same set, to enable the animal the more readily to use its hind legs in 

 regaining an ordinary position when suspended by the tail. Its two insertions appear to 

 relate to those rotatory movements of the limb that begin at the knee and culminate at the 

 ankle ; when acting together they antagonize each other, and result in simple flexion. 



Biceps. — (Fig. 32, d, d.) The fibular flexor of the leg has none of the characters that 

 suggested its name in human anatomy. Its " short " or femoral head is wanting j it has 

 no connection whatever with the femur. It arises from the tuber ischii by a short, stout 

 tendon, common to the semitendinosus ; it is separated from the femur by the quadratus 

 femoris and adductor magnus ; the continuation of the femoro-coccygeus separates it from 

 the vastus externus. Beyond the insertion of the glutseus maximus, the biceps is in inti- 

 mate relation, by its upper border, with the femoro-coccygeus; the aponeurotic insertion of 

 the latter into the leg is a part of the expansive tendon of the biceps. Similarly, the 

 lower border of the biceps is in relation with the cruro-coccygeus, after the latter has inos- 

 culated with the semitendinosus, and the aponeuroses are completely blended. The biceps 

 becomes thinner and wider as it proceeds to the leg, almost covering all the other flexors in 

 the lower part of its course ; and finally expands into a very broad and thin aponeurosis, 

 which, blended above and below with the similar fibrous expansions of the two coccygeals, 

 covers the outside of the leg from the knee nearly half way to the ankle. This fibrous 

 lamina has no direct insertion into the fibula ; it may readily be lifted in its entirety from 

 this bone, and traced around the leg as far as the crest of the tibia, which is its real final 

 attachment. It becomes lost, in fact, in the common fascia of the leg, and ligaments of the 

 knee joint. The diffuse indefinite insertion of the three flexing tendons on the outside of 

 the leg is in striking contrast to the rigidly determined and exact insertion of the four that 

 pass to the inner side. The want of two distinct heads of this crural flexor heightens its 

 similarity to the corresponding muscle of the arm. The resemblance is increased in a 



