448 Zoological Society : — 



hemispherical and large ; and the hase of the skull has a very ex- 

 quisite structure, which deserves full description, as it exceeds any- 

 thing we have seen in birds, the Heron making the nearest approach 

 to the Balceniceps in this particular. Many other birds, however, 

 show traces of this peculiar structure. The lower jaw is exceed- 

 ingly strong and thick, as compared with that of the Adjutant. 

 Less elliptical and more triangular than that of the Boatbill, it 

 lias, nevertheless, many of the characters of the latter. Its tip is 

 curiously emarginate, as is also the tip of the upper jaw — the bony 

 basis of the great hooked beak. The traces of suture between the 

 dentary and other elements of the mandible, which are persistent in 

 the Boatbill, Adjutant, and most other birds, are all filled up with 

 bony matter, as is the case in the Parrot tribe, in the Hornbills, and 

 in the Toucans. The anterior part of the mandible passes within the 

 maxilla, the edge of its horny sheath fitting between the marginal and 

 submarginal ridges of the latter. Where the upper jaw begins to 

 narrow towards its angle, there the mandible rises high (its height 

 or depth here being 1£ inch), and it is rounded, rough, and strong. 

 It then lowers again, and becomes rapidly broader, to form the deep 

 and wide articular cavities for the tympanic bone above, and the 

 broad flat angular processes behind and below. 



Each ramus of this great inelastic mandible is united to its fellow 

 at the symphysis by complete bony union to the extent of 1^ inch. 

 In the extremely elastic mandible of the Pelican this line of bony 

 union is cne-eighth of an inch in length, in the Boatbill one-fourth 

 of an inch, in the Adjutant 4| inches, and in the Hornbill, Buceros 

 bicornis, more than 7 inches. 



In the Boatbill and Grey Heron there are twenty-three separate 

 vertebras between the head and the pelvis ; in Balceniceps rex and 

 the Adjutant twenty-one, and in the White Stork twenty. 



In the Boatbill there are nine pairs of free ribs. The last, or pelvic, 

 does not reach the sternum, nor do the first four ; so that there are 

 four true dorsal ribs. In the Heron there are eight pairs ; the an- 

 terior three and the last (which is pelvic) do not reach the sternum : 

 here there are only four true dorsals. The Balceniceps, the White 

 Stork, and the Adjutant have each seven pairs of free ribs, the last 

 five reaching the sternum ; in Balceniceps and the Adjutant the last 

 pair are pelvic ; in the White Stork the last two pairs. Until the 

 birds are adult, the anterior vertebrae of the pelvis are but partly 

 united. In the Storks, Herons, Boatbill, and Balceniceps the dorsal 

 vertebrae continue distinct throughout life ; but in many of the Cranes 

 the tendons of the dorsal muscles are ossified, and fasten the bones 

 more or less together, and two or three contiguous centra coalesce. 

 Among the cervical vertebras of the true Herons and their nearest 

 allies, e. g. Arclea, Botaurus, Cancroma, and Balceniceps, there are 

 several which have elegant bridges under their upper or cranial end 

 for the carotid arteries, which bony bridges are not true hoemal 

 arches, but are formed by exogenous processes*. In these ver- 



* See Prof. Owen's article in Orr's ' Circle of the Sciences,' entitled " Structure 

 of the Skeleton and Teeth," p. 182, fig. 10. iv. 



