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, I.e. 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 pleur -apophysis, pi, 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 ham- 

 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 52, 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 hamiapophysial 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 

 haemal 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 

 or^an, 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 hsemal arch of the occipital segment of the skullf. 



* Bell (Sir Charles), " The Hand." Bridgewater Treatise, 1833, pp. 16, 18. 



M-Ovov ce kcu diifiSe'^iov yiyverai tujv aWwv £wa)v avOpwTros. — Aristotle. 



f 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 anus,' — ' but who 

 had clavicles and scapulae.' Here development was arrested at the point at which it is normal 



