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Show 1901.] ANATOMY OF P1CARIAN BIRDS. 21 is only to be seen in B. cafer. I consider this plate of bone arising from the pterygoid to be the homologue of the rudimentary articular facet of Buceros, but increased in a different direction. As is sometimes seen with degenerating organs, it has as it were run to seed. That it does not point toward the basipterygoid may perhaps be put down to the straightening and consequent rotation of tho pterygoid. The majority of these differences also hold good for other genera of arboreal Hornbills. The distinction between the cancellated boue which fills the casque, the maxilla, and between the posterior and anterior regions of the core of the. casque is apparent even in the almost casque-less Aceros. The really casque-less Toccus may be left out of consideration. The principal feature in which the skulls of other Hornbills are less marked than Buceros are the lower elevation of the brain-case and the comparative straightness of the pterygoids. Pelvis of Bucorvus and Buceros.-The pelves of the two species of Bucorvus agree exactly in the proportions of the pre-and of the post-acetabular regions. But when the genus is compared with Buceros, differences appear. In the latter genus the two regions of the pelvis which are separated by the antitrochanter are as nearly as possible equal in length; in Bucorvus the posterior region of the pelvis is rather the longer. This difference is coupled with another, viz., the greater depth of the ischia of Buceros, and the consequently more acute angle formed by the pubes with the longitudinal axis. In Bucorvus the pubes slope more nearly parallel to the long axis of the pelvis. One cannot but put down this difference to the difference in mode of life exhibited by the two genera. Hind Limb.-Measurements of the proportions of the several sections of the hind limb in the two species show some slight differences which are perhaps worthy of being recorded. In Bucorvus abyssinicus the measurements were as follows: femur 110 m m . ; tibia 200 m m . ; metatarsus 157 mm.; middle toe 90 m m . Of B. cafer the corresponding figures were 100 ; 185; 135; 77. Hind limb of Bucorvus and Buceros.-It is of course well enough known that the Ground-Hornbills have longer legs than the arboreal genera; but nevertheless a few exact measurements may be useful. I append therefore a number of such measurements (in millim.), which have been taken in every case from the dried skeleton :- Femur. Tibia. Metatarsus. Middle toe. Buceros rhinoceros 90 125 62 77 Rhytidiceros plicatus 74 102 49 62 Dichoceros bicornis 108 141 71 80 It is plain from these measurements that the tibia is shorter relatively to the femur in the flying Hornbills, and that the metatarsus iii the same birds is shorter relatively to the tibia than in the Ground-Hornbills. Taking the femur in all cases as 1, the |