390 
EASTERN ETHIOPIA 
XXXI 
A lierd of elephants is often accompanied by a flock 
of bnfl-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 tusks of the elephant grow throughout life, for 
they possess persistent pulps like the incisors of rats 
and rabbits, and the only check to their length is the 
wear and tear to which they are subjected in digging 
up roots, uprooting small trees, or stripping them of 
bark : one tusk is used more than tlie other, usually 
the right, and is called for this reason the servant by the 
Arabs. They are also used for offence and defence, and 
vicious bulls sometimes break their tusks fio^htin^ rivals. 
In Equatorial Africa tiie elephant attains its greatest 
size. A. H. Neumann o:ives the averas^e height 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 of Ehjyhas africanus 
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 basal portion lodged 
in the bone of the upper jaw, and a portion which pro¬ 
jects beyond the animal’s lips. When 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 basal 
part will be found to consist of a conical chamber, the 
walls of which, near its wide extremity, are very thin. 
The remaining two-thirds are solid, but a close examina- 
