Lect. II.] FORMATION OF THE LOWER JAW. 41 



grafting purposes — a mass of cartilage wliicli we are 

 not familiar with in the reptile or the bird. 



Looking for a slab of true hyaline cartilage large 

 enough for Nature's purposes in these mammalian types, 

 we travel down through Birds, Eeptiles, Amphibia, 

 Osseous Fishes, Ganoids, Skates, and ordinary Sharks, 

 and not until we come to the extraordinary Sharks or 

 Chimseroids do we find anything large enough. There 

 we stop. In these waifs of an old fish fauna we do light 

 upon what is wanted. In these fishes there is, outside 



Fia. 6. — Mandible (Lower Jaw) of an Embryo Pig, 3 inches long, magnified Si- 

 diameters ; inner view. mk, Meckel's cartilage ; d, dentary bone ; cr, coronoid 

 process ; ar, articular process (condyle) ; ag, angular process ; ml, malleus ; inb, 

 manubrium. 



the true mandible, a large slab of cartilage equal to it 

 in size. This is a superficial (subcutaneous) band of 

 solidified tissue, but it has no supporting bone on it. 

 Such a supporting bone, however, is seen clearly enough 

 in the foremost of the splints of the lower jaw (the 

 dentary) in all fishes, except the cartilaginous kinds, 

 and in all types above the fishes. Besides this, on the 

 inside of the fore part of the lower jaw, in the o\dparous 

 types, there is a second splint, the splenial, and Ijchind 



