OCR Text |
Show 1880.] MR. W. A. FORBES ON LEPTOSOMA DISCOLOR. 471 the same muscle in the Coraciidae. In no other birds amongst the Anomalogonatae is this muscle present. In the Cuculidae this muscle is present, but its terminal tendon is not T-shaped, the sternal moiety being undeveloped. The arrangement of the termination of the tensor patagii brevis is represented in the accompanying figure (tig. 2, p. 470). The main tendon (t.p.bri) runs on to the ulnar side of the arm, and there becomes fused with the fascia covering the muscles. Before doing so, however, it crosses the superficial tendon of origin of the extensor metacarpi radialis longior (e.m.ri), which springs from the humeral tubercle, and becomes firmly blended with it. It likewise sends off, distally, a special slip of tendon which joins the same tendon of that muscle more externally (wristward). This is much the same arrangement as in the Coraciidae, as described and figured by Prof. Garrod (P. Z. S. 1876, p. 511, pl. 49. fig. 1), except that in those birds the tendon of the tensor patagii brevis is split into two quite separate halves; if these were united together, an arrangement would be arrived at practically identical with that of Leptosoma. In the Cuculidae the condition of things is quite different, as in them the " undivided tendon runs on to the ulnar superficial fascia without any complication" (/. c. p. 512). Of the leg-muscles, the gluteus primus is present, though small, only slightly overlapping the biceps, and with its fleshy part not reaching the innominate, to which it is attached only by fascia. The ambiens is absent; the femoro-caudal is very large, but lacks the accessory head, as in all Anomalogonatee. Both the semitendinosus and its accessory are well developed, as is the semimembranosus. The biceps cruris, as usual, passes through a tendinous loop. The obturator externus is well developed, and the obturator internus is of a very elongated oval shape. The formula of Leptosoma is therefore - . A . X . Y, exactly the same as that of the Coraciidae and the greater number of Anomalogonatous birds. In the Cuculidae the ambiens is always present and well developed, and the accessory femoro-caudal usually so1, giving a formula of + . A . ( B ) . X . Y . Leptosoma is therefore clearly not Cuculine. In the Cuculidae, too, the obturator internus is triangular in shape, as in the Gallinae and their allies ; in Leptosoma, as already stated, as in Coracias, it is oval. The anomalous arrangement of the toes in Leptosoma made me very anxious to observe the disposition of its deep plantar tendons, these, in all " zygodactyle " Anomalogonatous birds, being arranged in a manner quite unique amongst birds and entirely different from that which obtains in the even-toed Homalogonatous birds (i. e. the Psittaci, Cuculidae, and Musophagidae)2. But in Leptosoma neither of these conditions occurs; on the contrary, the disposition of its plantar tendons is exactly that found in many birds with feet of the ordinary structure. This condition is 1 It is absent only in Cuculus, Chrysococcyx, and Cacomantis. [Garrod's MSS.] 2 Vide Garrod, P. Z. S. 1875, p. 345. |