390 EASTERN ETHIOPIA xxxi 



A herd of elephants is often accompanied by a flock 

 of buff-backed herons. When the herd moves the 

 herons follow on the wing, and hover over, or on its 

 flanks, like a white cloud. When the elephants are at 

 rest, or feeding, these birds alight, and rid them of 

 vermin. In reference to this, Livingstone wrote : the 

 ox-pecker is a better horseman than the heron, for it 

 sits on the withers of a buffalo when the animal is at 

 full speed (see p. 193). 



The tusk.s of the elephant grow throughout life, for 

 they j^ossess persistent pulps like the incisors of rats 

 and rabbits, and the only check to their length is the 

 Avear and tear to which they are sul)jected in digging 

 up roots, uprooting small trees, or stripping them of 

 bark : one tusk is used more than the other, usually 

 the right, and is called for this reason the servant by the 

 Araljs. They are also used for offence and defence, and 

 vicious bulls sometimes l)reak their tusks fio-htino- rivals. 

 In E(]uatorial Africa the elephant attains its greatest 

 size. A. H. Neumann oives the averaoc heioht of the 

 full-grown bull elephant at 10^ feet. The tusks of 

 such an animal may weigh anything from 50 to 100 

 pounds, or more. There is a tusk oi Elcphas africmms 

 in the Natural History Museum 10 feet long and 2 feet in 

 girth ; it weighs 228 pounds. Although tusks are 

 present in both sexes of elephants, they are much larger 

 in the male. 



A tusk consists of two parts ; a liasal portion lodged 

 in tlie bone of the upper jaw, and a portion wliicli pro- 

 je(;ts l)eyond the animal's lips. Wlicn an elephant is 

 killed, it is wise not to attempt to chop out the tusks 

 at once, as this injures the ivory : in a few days, the 

 tusks loosen and are easily removed. 



When a dried tusk is split longitudinally its Ijasal 

 part will be found to consist of a conical chaml)er, the 

 walls of which, near its wide extremity, are very thin. 

 The remaining two-thirds are solid, but a close examina- 



