1901.] AJTATOMT OF PlCARIA]!f BIRDS. 21 



is oul_y to be seen in B. cafer. I consider this plate of bone arising 

 from the ptervgoid to be the homologue of the rudimentary arti- 

 cular facet of Buceros, but increased in a different direction. As is 

 sometimes seen with degenerating oigans, 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 

 bone which tills 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 Bviceros. — The pelves of the two species 

 of Bucorviis 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 

 hmgitudinal axis. In Bucorvus the ])ubes 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 

 tv\'o genera. 



Hmd Limb. — Measurements of the proportions of the several 

 sections of the hind limb in the two species show some slight 

 diffei'ences which are perhaps worthy of being recorded. In 

 Bacor^vus ahyssinicusX\\e measurements were as follows: femur 

 110 mm. ; tibia 200 mm.; metatarsus 157 mm.; middle toe 90 ram. 

 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 Grround-Hornbills have longer legs than 

 the arboreal genera ; but nevertheless a few exact measurements 

 may be useful. I append therefore a number of such measure- 

 ments (in millim.), which have been taken in every case from the 

 dried skeleton : — 



Femur. 



Buceros rliinoceros 90 



Bhytidiceros plicaius .... 74 

 Diclwceros hicornis 108 



It is plain from these measurements that the tibia is shorter 

 relatively to the femur in the flying Hornbills, and that the meta- 

 tarsus in the same birds is shorter relatively to the tibia than 

 in the Grouud-Hornbills. Taking the femur in all cases as 1, the 



