i 
ON THE VERTEBRATE SKELETON. 301 
development of the parapophysis. This, as in other mammals, is not only an 
exogenous process of the neurapophysis, 2, but is commonly reduced to a 
mere “ scabrous ridge extended from the middle of the condyle towards the 
root of the mastoid process” (Monro, J. ¢. p.’72)—the “ eminentia aspera 
musculum rectum lateralem excipiens” of Soemmerring: the knowledge of 
its general homology, however, makes quite intelligible and gives its true 
interest to the occasional development of this ridge into a ‘ paramastoid’ 
process, which now, however, projects, like the true ‘ mastoid,’ downwards 
from the basal aspect of the cranium (ante, p. 204). 
The occipital plewrapophysis, pl, 51, shows the same displacement as in 
other mammals, but is still more expanded in the direction of the trunk’s 
axis, and its exogenous (acromial) process is still more developed. The hem- 
apophysis (52), originally distinct, has its development checked and speedily 
coalesces with the pleurapophysis. 
If the bone 52! be the special homologue of the bone, ss, in the fish,—and 
considering the backward displacement of 51 and 5, its anterior position to 
them in man is no valid argument against the determination,—then we may 
adopt the same general homology, and regard the clavicle, in its relations to 
the vertebrate archetype, as the displaced hemapophysial element of the 
atlas, to which segment its true relative position is shown in the same low | 
organized class in which the typical position of the scapular arch is likewise 
retained. 
The adaptive developments of the radiated appendage of the occipital 
hemal arch reach their maximum in man, and the distal segment of the ap- 
pendage constitutes in him an organ which the greatest of ancient philoso- 
phers has defined as the “ fit instrument of the rational soul ;” and which 
the first of modern physiologists has described “as belonging exclusively to 
man—as the part to which the whole frame must conform”*. And these ex- 
pressions give no exaggerated idea of the exquisite mechanism and adjust- 
ment of its parts. 
It is no mere transcendental dream, but true knowledge and legitimate 
fruit of inductive research, that clear insight into the essential nature of the 
organ, which is acquired by tracing it step by step from the unbranched 
pectoral ray of the protopterus to the equally small and slender but bifid 
pectoral ray of the amphiume, thence to the similar but trifid ray of the 
proteus, and through the progressively superadded structures and perfec- 
tions in higher reptiles and in mammals. If the special homology of each 
part of the diverging appendage and its supporting arch are recognisable 
from Man to the fish, shall we close the mind’s eye to the evidences of that 
higher law of archetypal conformity on which the very power of tracing the 
lower and more special correspondences depend ? 
Until the alleged facts (p. 285) are disproved, demonstrating change of 
position to be one of the modifications by which parts of a natural and re- 
cognisable endoskeletal segment are adapted to special offices, and until 
the conclusions (p. 286) deduced from those facts are shown to be fallacious, I 
must retain the conviction that, in their relation to the vertebrate archetype, 
the human hands and arms are parts of the head—diverging appendages of 
the costal or hemal arch of the occipital segment of the skull+. 
* Bell (Sir Charles), ‘“ The Hand.” Bridgewater Treatise, 1833, pp. 16, 18. 
Movoy 6é kai augoézvoy yiyverat Tw Gdd\wy Cowy avOpwros.— Aristotle. 
+ As another example of the new light and interest which a knowledge of general homo- 
logy gives to the facts of abnormal anatomy in the human species, I may cite the remark- 
able case described by Sir C. Bell (op. cit p. 52), of the boy ‘ born without arms,’— but who 
had clayicles and scapule.’ Here development was arrested at the point at which it is normal 
