1901.] ANATOMY OF PICARIAN 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's - almost contemporaneous investigations 

 upon the same subject. The latter work contains, naturally, a 

 number of facts relating to the slieleton 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 ^ and myself^ 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 vertebras in both birds) is shorter than that of 

 B. abysslnicus. 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 expression 

 of a smaller-sized bird, since the dorsal vertebrae are of exactly the 

 same length collectively and individually in 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. abyssinicus. Though firmly welded to its vertebra, the 

 homologue of the rib is more slender, as is the case 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 notj however, free itself. The rib is long and 

 slender. 



Vertebral Column of Bucorvus compared luith other Hornbills. — 

 The great breadth and excavation below of the cervical vertebra 

 distinguish Bucorvus from Buceros. There are, moreover, thirteen 

 of them, while in Buceros the thirteenth vertebra bears a small but 

 movable rib on each side. In Bucorvus there are no closely- 

 approximated catapophyses ; in Buceros \he 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 xiphisteruum is liot nearly so deep as in B. cafer. 



^ " On some Poiiits in the Structure of the Hornbills," P. Z. S. 1889, p. 587. 



2 ' Untersueliung. zur Morph. d. Vogel,' Amsterdain, 1888. 



' Bi-oun's • Ordnungen des Tierreiclis,' Avos. 



* ' The Structure and Classification of Birds,' Longmans, 1896. 



Pkoc. Zool. Soc— 1901, Vol. I. No. II. 2 



