OCR Text |
Show 96 ON THE ANATOMY OF THE TOUCANS AND BARBETS. [Jan. 3, by a tendinous slip into a small tubercle on the external surface of that bone, close to the elbow, and just above the tubercle for the tendon of origin of the extensor metacarpi radialis longior muscle. This is common to the Picidae, Indicator, and the Toucans and Barbets. As long ago noticed by Nitzsch1, this peculiarly long deltoid also occurs in the Passeres ; but its similar condition in the Capitonidse has not, I think, before been observed. But, as showing that the similarity in this respect of the Passeres to the Picidae and their allies is not necessarily a mark of relationship, I may add that in some other birds, as, e. g., Carpophaga, Ptilopus, and Cariama, the deltoid is nearly the same in size and shape, extending down to very near the elbow. (2) The presence of a distinct ossicle, of the nature of a sesamoid, the so-called " scapula accessoria," which is developed in the scapulo-humeral ligament of the shoulder-joint, and plays over the posterior angle of the humerus-head. From it arise some of the fibres of the deltoid. Nitzsch, with his usual accuracy 2, had also noticed the existence in the Picidae of this bone, which, as is well known, occurs also in the Passeres; but the relationships of the bone in the last are not the same as they are in the Picidae, Indicator and other Pici I have examined. In the Passeres the bone in question becomes connected with the tendon of the pectoralis secundus muscle as this courses over the head of the humerus towards its insertion, sending round it a special thin tendinous loop, in which the tendon of that muscle plays. Hence, in the undisturbed position of these parts, the pectoralis tendon is seen to be somewhat L-shaped, the angle of the L being at the place where it is connected by this fibrous loop to the sesamoid bone, and so dragged backwards out of a direct course. In the Pici I have been able to find no such connection between the scapula accessoria and the pectoralis secundus tendon, which remains quite free from it throughout its course. The additional points of resemblance detailed in the present communication render the near relationship of the Picidae to the Capi-tonidae even more certain than before. Nitzsch, from pterylographical grounds, and Kessler 3, from osteological ones, long ago pointed out this connection, which was afterwards remarkably confirmed by Garrod's observations on their myology and visceral anatomy. The fact that there should be important cranial differences between the two groups (and even amongst the members of one of these) only shows that the cranial structure of a bird may be profoundly changed, in accordance with its conditions of existence, whilst in the rest of its organs no change whatever is effected ; and such a fact must of itself tell heavily against the view that the structure of the skull in birds is of itself alone a certain, or even sufficient, index to their systematic classification. 1 Zeitschr. f. ges. Naturwiss. 1862, xix. p. 400. 2 Tom. supra cit. p. 399. 3 Bull. Soc. Imp. Nat. Moscou, xvii. pp. 332-334, 340. |