of the, Verteb)'ate Skeleton. 39 



sume that Avhen, in the mammal, one continuous ossification 

 joined up all the splint elements of the lower jaw, the os arti- 

 eulare and quadrate bone, as natural elements of the same rib, 

 could be no exception, and that there is nothing more re- 

 markable in this union than in any of the other transitions to 

 simplicity and uniformity and order which are produced by 

 j)otential groAvth. 



And it may not be uninteresting to remark how much the 

 vertical part of the lower jaw in any herbivore reproduces of 

 the form of the quadrate bone in such an animal as a bird, 

 and lioAv the inflection of the lower jaw in marsupials and 

 rodents reproduces such an inflexion as characterizes the os 

 articulare in birds and many reptiles. These growths in the 

 mammal may, I conceive, be potential repetitions. In the 

 mammal the pterygoid is moderately developed and is directed 

 downward posteriorly, and not backward as in birds and 

 lizards ; so that it does not actually meet the representative of 

 the quadrate bone ; but the union is kept up by the ptery- 

 goideus muscle, attached from the outer inferior side of the 

 pterygoid to the inner side of the quadrate portion of the 

 lower jaw. 



I am aware that Prof. Huxley has supposed that, contrary 

 to all analogy, the quadrate bone and os articulare enter the 

 mammalian cranium and become the malleus and incus. 

 After reading all that has been said for that doctrine, I can 

 see no evidence in its favour sufficiently strong to dissuade me 

 from stating my own view. If it has been important to con- 

 struct those bones out of pre-existing cranial elements, I would 

 suggest that Prof, Huxley might have taken the quadrato- 

 jugal and symplectic, which were available and would have 

 answered equally well. But I do not think any exigency of 

 theory can justify the creation of a new joint in the body by 

 imagining a convex articulation beneath the articular bone, 

 when there is nothing in the vertebrate province to suggest 

 that such an articulation might exist. 



Such, divested of details, is the conception of the common 

 plan of the axial skeleton which, by the operation of the laws 

 of organic energy, may, I believe, call all skeletons into exis- 

 tence, extending them over the viscera like a pillow-case over 

 a piUow, till the animal is gradually but inevitably sheathed 

 in rings of bones. And thus it will be remarked that the pre- 

 existing soft animal would have no necessary correlation of 

 soft vital parts with its osseous sheath. 



I touch with reluctance, because of its difiiculties, on another 

 part of the skeleton, which seems as though only appended to 

 the vertebral column, already discussed by Prof. Owen, in his 



