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Show 1901.] ANATOMY OP PIC'ARIAN BIRDS. 17 since I have nothing new to add to my ' earlier account of the muscles and the viscera of Bucorvus and other genera of Hornbills, or to Prof. Fiirbringer's2 almost contemporaneous investigations upon the same subject. The latter work contains, naturally, a number of facts relating to the skeleton of the Hornbills in general, as well as of Bucorvus ; but these, as might be expected, deal chiefly with the shoulder-girdle. Another source of information concerning the bones of the Bucerotidae is Mr. Eyton's ' Osteologia Avium,' which work includes figures of the skeletons of Bucorvus and of a few other forms together with some quite brief notes in the text. The family is of course not neglected in the general works of Dr. Gadow 3 and myselfl upon bird-anatomy. There is, however, at least so far as I am aware, no account of the bones of the two species with which I deal here-no comparison of the two forms. Vertebral Column.-Only two features in the vertebral column distinguish the two species of Bucorvus. In the first place, the relative lengths of the several regions differ: in Bucorvus cafer the cervical series (13 vertebrae in both birds) is shorter than that of B. abyssinicus. The total difference of length is rather more than an inch, and each individual vertebra is distinctly shorter than the corresponding one of the other species. This is not an expressiou of a smaller-sized bird, since the dorsal vertebrae are of exactly the same length collectively and individually iu the two species. Nor is there any difference except the very minutest in the lengths of the sacral and,caudal series. The last cervical vertebra of B. cafer has a transverse process which is slightly more rib-like than is that of B. abijssinicus. Though firmly welded to its vertebra, the homolegue of the rib is more slender, as is the ca?e in those birds where it is a free structure. The second point of difference concerns the presence of an additional rib in B. cafer at the end of the series. The vertebra bearing that rib is not, however, free itself. The rib is long and slender. Vertebral Column of Bucorvus compared with other Hornbills.- The great breadth and excavation below of the cervical vertebrae distinguish Bucorvus from Buceros. There art1, moreover, thirteen of them, while iu Buceros the thirteenth vertebra bears a small but movable rib on each side. In Bucorvus there are no closely approximated catapophyses ; in Buceros the 11th vertebra has a pair of these. The remaining salient characteristic of Bucorvus is the slenderness of the pygostyle, which might be expected in a ground-living bird. Sternum.-The only difference that I could detect between the sterna of the two species was that in B. abyssinicus the lateral incision of the xiphisternum is not nearly so deep as in B. cafer. i " On some Points in the Structure of the Hornbills," P. Z. S. 1889, p. 587. 2 ' Untersuchung. zur Morpli. d. Vogel,' Amsterdam, 18S8. 1 Bronn's ' Ordnungen des Tierreichs,' Aves. 4 ' The Structure and Classification of Birds,' Longmans, 18%. P R O C ZOOL. Soc-1901, VOL, I. No. Ii. 2 |