ON THE THEORY OF THE VERTEBRATE SKULL 539- 



Studied without bearing witness to the truth of these propositions. 

 The tyro in comparative anatomy cannot fail to be struck with the 

 resemblances between the leg and the jaw of a crustacean ; between 

 the parts of the mouth of a beetle and those of a bee ; between the 

 wing of the bird and the fore-limb of the mammal. Everywhere he 

 finds unity of plan, diversity of execution. 



Or again, how can the intelligent student of the human frame 

 consider the backbone, with its numerous joints or vertebra, and 

 trace the gradual modification which these undergo downwards into 

 the sacrum and coccyx, and upwards into the atlas and axis, without 

 the notion of a vertebra in the abstract, as it were, gradually dawning 

 upon his mind ; the conception of an ideal something which shall 

 be a sort of mean between these various actual forms, each of which 

 may then easily be conceived as a modification of the abstract or 

 typical vertebra? 



Such an idea, once clearly apprehended, will hardly permit the 

 mind which it informs to rest at this point. A glance at a section 

 of that complex bony box formed by the human skull and face, 

 shows that it consists of a strong central mass, whence spring an 

 upper arch and a lower arch. The upper arch is formed by the 

 walls of the cavity containing the brain, and stands in the same 

 relation to it, as does the neural arch of a vertebra to the spinal cord,, 

 with which that brain is continuous. The lower arch encloses the 

 other viscera of the head, in the same way as the ribs embrace those 

 of the thorax. And not only is the general analogy between the two 

 manifest but a young skull may be readily separated into a number of 

 segments, in each of which it requires but little imagination to trace a 

 sort of family likeness to such an expanded vertebra as the atlas. 



What can be more natural then than to take another step — to con- 

 ceive the skull as a portion of the vertebral column still more altered 

 than the sacrum or the coccyx, whose vertebrae are modified in corre- 

 spondence with the expansion of the anterior end of the nervous 

 centre and the needs of the cephalic end of the body, just as those 

 of the sacrum are fashioned in accordance with the contraction of 

 the nervous centre and the mechanical necessities of the opposite 

 extremity of the frame ? 



Two generations have passed away since, perhaps, by some such 

 train of reasoning as this, such a conception of the nature of the 

 vertebrate skull arose in the mind of the philosophic poet, Goethe ; 

 and a somewhat shorter period has elapsed since a poetical, or per- 

 haps I might more justly say a fanciful, philosopher, Oken, published 

 a " Theory of the Skull " embodying such a conception ; and since 



