1022 ON FORM AND MECHANICAL EFFICIENCY [ch. 



which has been taken away^^ It fulfils this function by various 

 means; by the way in which the two sides of the girdle are conjoined 

 into a single arch ; by its strong attachment to the head, and again 

 to the pelvis, and through the latter to the chain of ossicles which 

 bound or constitute the abdominal border of the fish ; and a large 

 part of the stress upon the shoulder-girdle proper is taken up, or 

 relieved, by the strong post-clavicular bones, which form a supple- 

 mentary arch running downwards from the clavicle (just where it 

 begins to incline forward), straight to the ventral border, to be 

 firmly attached there to the ventral ossicles. Similarly we notice 

 at the hinder border of the abdominal cavity, a strong curved bone 

 running from the anterior part of the ventral fin to a solid attach- 

 ment with the vertebral column, stiffening the ventral part, and 

 helping the shoulder-girdle to restore full strength to the girder 

 after it had been reduced, so to speak, to the brink of inevitable 

 collapse. The skull itself is not only streamlined with the rest of the 

 body, but is an intrinsic part of the whole engineering construction. 

 The lines of stress run simply and clearly through the skeleton, and 

 a bone can no longer teach us its full and proper lesson after we have 

 taken it apart. To look on the hereditary or evolutionary factor 

 as tlie guiding principle in morphology is to give to that science 

 a one-sided and fallacious simplicity*. 



It would seem to me that the mechanical principles and phenomena 

 which we have dealt with in this chapter are of no small importance 

 to the morphologist, all the more when he is inclined to direct his 

 study of the skeleton exclusively to the problem of phylogeny ; and 

 especially when, according to the methods of modern comparative 

 morphology, he is apt to take the skeleton to pieces, and to draw 

 from the comparison of a series of scapulae, humeri, or individual 

 vertebrae, conclusions as to the descent and relationship of the 

 animals to which they belong. 



It would, I dare say, be an exaggeration to see in every bone 

 nothing more than a resultant of immediate and direct physical or 

 mechanical conditions ; for to do so would be to deny the existence, 



* The extreme evolutionary, or phylogenetic, aspect of morphology was being 

 questioned even forty years ago. "Where we once thought we detected relation- 

 ships we now know we were often being misled, and the old-time supposition 

 that mere community of structure is necessarily an index of community of origin 

 has gone to the wall" (G. B. Howes, in Nature, Jan. 10, 1901). 



