20 MB. r. E. BEDDARD ON THE [Jail. 15, 



of bone to form a proiecting ridge which joins the jugal arch behind. 

 This renders the margins of the orbit perfectly visible when the 

 skull is viewed directly from the front. In Buceros there is no 

 such ridge, and the orbit is invisible when the skull is h)oked at 

 from in front. , ... 



The narial aperture is double on each side in Bmorvus as it is in, 

 for example, the Toucans. Each of the two apertures into which 

 the originally single aperture is divided in this genus is of a rather 

 elongated oval outline. In Buceros the single narial orifice is 

 circular in outline. 



A comparison of the dorsal aspect of the skull in the two genera 

 shows several points of divergence in the two types. The greater 

 breadth of the cranium of Buconms is apparent, this being mainly 

 due to the projecting shelf of bone over the orbit, already referred 

 to. furthermore the " lacrymal " ring in front of the orbit which 

 is absent or at least not so fully developed in Buceros, causes a 

 very sharp demarcation between the cranium and the face in Bu- 

 corvus, a distinction which is wanting in Buceros, where one region 

 gradually fades into the other. The commencement of the beak 

 region is quite as wide as the anterior part of the ovh\t in Buceros ; 

 in Bucorvits it is very plainly much narrower. The contrast is so 

 great that measurements are unnecessary to express the differences. 



The basal aspect of the skull of Bucorvns is in some respects 

 different from that of Buceros. In the iirst place, the foramen 

 magnum in Bmorvus is much more distinctly upon the ventral sur- 

 face than in Buceros, where this foramen looks partly backwards. It 

 thus happens that the dorsal wall of the foramen is more apparent 

 on a dorsal view in Buceros than it is in Bucorvus. The palatal 

 region too shows differences which are not without a certain interest 

 in relation to the connection between the two types of Hornbill. 

 As has been already recorded by Fiirbringer, the Bucerotidse 

 possess basipterygoid processes. These are, however, rudimentary, 

 and are far from being in contact with the pterygoids. In Buceros 

 ]iot only are there present a pair of somewhat jagged rudimentary 

 basipterygoid processes, but the pterygoids themselves are bowed 

 inwards opposite to these processes ; at the place where they should, 

 so to speak, articulate with the basipterygoid processes they bear 

 a roughened outgrowth which seems to suggest the remains of a 

 pterygoid articular facet. 



vSo exactly does the position of this facet correspond to the 

 basipterygoid process, that if the bones could be forcibh' pushed 

 toge-her they would meet at those points. Bucorvus shows a 

 further stage of degeneration, which fits in well with the presump- 

 tion that it is a later type than Buceros. The basipterygoid pro- 

 cesses are distinctly more rudimentary, and, indeed, they are only 

 just recognizable in B. ahyssinicus. The pterygoids are straight, 

 and are not at all bowed inwards towards the basipterygoid pro- 

 cesses. In the place of what I have regarded as an articular 

 facet upon the pterygoids in Buceros, there is in Bucorvus a thin, 

 large, upwardly directed lamellar pro-ess of bone. This, however. 



