Chapter V

PROOFS FROM HOMOLOGIES OF THE VERTEBRATE SKELETON.

_Common general plan_--In several respects--Strongly suggestive of
common origin--Details of structure demonstrative of the same 111

_Special homology of vertebrate limbs_ 113

_Fore-limbs_--Comparison of fore-limbs of mammals, birds,
reptiles, and fishes, part for part--Gradual changes in
collar-bone and coracoid--In position of elbow--In bones
of forearm--In position of wrist--In the tread--The term
manus--Number of toes--Modifications for flight in various
animals--For swimming in whales and fishes 113

_Hind-limbs_--Comparison of hind-limbs of several mammals--
Position of knee--Of heel--Plantigrade and digitigrade
--Degrees of the latter--Number of toes--General law in
regard to number of similar parts--Order of toe-dropping in
artiodactyles--In perissodactyles 121

_Genesis of the horse_--Changes in foot-structure--Same true
of other parts of skeleton--Only natural explanation is
derivation--Nature compared with man in mode of working--
Angels--Griffins--Centaurs--Muscular and nervous systems
--Visceral organs 126

CHAPTER VI.

HOMOLOGIES OF THE ARTICULATE SKELETON.

_Illustrations from this type_--Plan of structure entirely
different--General plan of structure explained and
modifications shown--Shrimp--Modification of segments and
of appendages for various purposes: swimming, walking, eating,
sense--Illustrated by other crustaceans--By myriapods--
By marine worms--Crabs--Embryonic development of crabs--
insects--Modification of segments and appendages--Mouth
parts of insects 132

_Illustration of the law of differentiation_--Cells--Segments
--Individuals--Homologies in other departments of animals,
but these are less familiar--Between primary groups, homology
untraceable in adult forms--But these also probably connected
by common origin--Different views as to origin of vertebrates 144