362 On a Theory of the Skull and the Skeleton. 



the face, extending over the maxillaries, but entering, as in birds 

 and Ichthyosaurs and most animals, into the anterior nares. In 

 ruminants and pachyderms, where the pressure from the teeth 

 is more uniform than in some animals, it is seen that the maxil- 

 laries are deep and their upper and lower margins subparallel; 

 and, as though illustrating the community of origin, in some 

 animals the palatines and pterygoids both bear teeth. The 

 bones forming the elements of the oviparous lower jaw I believe 

 to have been developed as epiphyses of MeckeFs cartilage by 

 pressure ; the dentary element presents the aspect of a terminal 

 epiphysis, and the four other bones a superior and inferior and two 

 lateral epiphyses, which functionally are a diapophysis. And now, 

 of the important elements of the skull, there only remain the eyes 

 and the ears, which correspond, in their relations to the ali- 

 sphenoid, with the intervertebral nerves. The growth of the 

 eye is a sufficiently evident cause of pressure to account for 

 sclerotic, superorbital, and lachrymal bones ; but the periotic 

 bones, which have been so laboriously elaborated by Pro- 

 fessor Huxley, appear to me to be nothing but ossifications 

 around the auditory canals which have afterwards grown by 

 contact with other ossifications. The quadrate bone is large 

 when placed between the jaw and the skull, but dwindles to the 

 incus when the pressure is removed ; and so the mastoid, squa- 

 mosal, and petrosal obviously owe their development to their rela- 

 tions with the jaw. They are clearly sense-bones, and therefore, 

 forming no part of the skull except as such, may be here passed 

 over without further notice. 



Such, then, is an outline of the mechanical theory of the skull ; 

 and such are some of the chief points which I hope to illustrate 

 and demonstrate in the collections of fossil vertebrata which are 

 among the best treasures of the Woodwardian Museum. This 

 theory difi^ers from others in the subordination of structure to func- 

 tion, and the belief that, except for the variation in organization, 

 similar functions will always develope similar structures. It difi'ers 

 from other theories in giving a mechanical reason for the presence 

 of every bone. Its final conclusion is, that the skull is the terminal 

 segment of the body, and that, just as the adjacent segments 

 consist of the pharynx, the larynx, and a vertebra enclosing part 

 of the neural column, so also the skull, which is the termina- 

 tion of these three organs, and where their outlets are visible, 

 must consist of them also; that the brain-case, therefore (the 

 termination of the neural system), is a modified vertebra, that 

 the bronchial circle of nasal and palatine bones is a modification 

 of the trachea, and that the lower jaw is a modified rib developed 

 by the mouth. The respiratory circle of bones is the key to the 

 skull. 



