The Descent of Man

des of the lower mandible are peculiar to the
male sex." (64. 'Land and Water,' 1868, p. 217.)
The head, again, often supports fleshy appendages,
filaments, and solid protuberances. These,
if not common to both sexes, are always
confined to the males. The solid protuberances
have been described in detail by Dr. W. Marshall
(65. 'Ueber die Schadelhocker,' etc., 'Niederland.
Archiv. fur Zoologie,' B. I. Heft 2,
1872.), who shews that they are formed either
of cancellated bone coated with skin, or of
dermal and other tissues. With mammals true
horns are always supported on the frontal bones,
but with birds various bones have been
modified for this purpose; and in species of the
same group the protuberances may have cores
of bone, or be quite destitute of them, with intermediate
gradations connecting these two
extremes. Hence, as Dr. Marshall justly remarks,
variations of the most different kinds
have served for the development through