200 



SCIENCE. 



[N. S. Vol. XIV. No. 345. 



other relation except one to be mentioned 

 immediately, goes to prove that it is the 

 equivalent of the articular. In the forma- 

 tion of the malleus a membrane bone is 

 concerned. This arises in front of the 

 articular -proper on the inner and lower 

 side of the cartilage — that is, in the right 

 position for the angular — and forms the 

 process Folianus of the malleus. At some 

 distance from the malleus two membrane 

 bones form the lower jaw of the adult. 

 The larger of these, from its relations and 

 position, is clearly the dentary, while the 

 smaller and inner one is as plainly the 

 splenial. Thus we can apparently recog- 

 nize in the mammalian lower jaw the artic- 

 ular and the three membrane bones most 

 constant in the lower vertebrates. In some 

 mammals, according to Parker, two addi- 

 tional membrane bones, each with its 

 equivalent in the lower vertebrates, are 

 said to occur. Besides all these there ex- 

 ists a patch of cartilage in either half of 

 the lower jaw which arises entirely inde- 

 pendently of the Meckelian, never unites 

 with it, and which is, so far as I know, 

 without any equivalent in any amphibian, 

 reptile or bird. 



To the identification of the bones of the 

 lower jaw which have just been given, there 

 is one very serious objection. The articu- 

 lation with the cranium is not homologous 

 with that of the lower vertebrates. After 

 the formation of all the bones of the jaw 

 the Meckelian cartilage becomes absorbed 

 between the Folian process and the hinder 

 margin of the dentary, leaving the jaw 

 proper without connection with the quad- 

 rate. The posterior portion of the dentary 

 extends up around the second cartilage men- 

 tioned, and articulates with the squamosal, 

 the dentary furnishing the articular condyle, 

 the squamosal the glenoid fossa. It is not 

 easy to say how this new articulation can 

 have been introduced, for it is hard to see 

 how an organ in constant use like the jaw 



could transfer its hinge from the quadrate to 

 the squamosal. And yet, from any point of 

 view, it seems impossible to escape the con- 

 clusion that it is not homologous with the 

 articulation of the lower vertebrates, for 

 the articulation in the non-mammalian 

 forms is at the proximal end of Meckel's 

 cartilage, while in the mammals the Meck- 

 elian does not come anywhere near the re- 

 gion of the glenoid fossa. Again, in the 

 glenoid fossa there is no trace of any carti- 

 lage which could be used as a basis for the 

 view that the quadrate has disappeared at 

 this point. 



A word about Albrecht's supposed quad- 

 rate may be inserted here, since it has often 

 been quoted in this connection. Albrecht 

 found, on one side of the skull of an idiot, 

 a separate bone in the region of the zygo- 

 matic process of the temporal bone, and 

 since the lower jaw articulates at this point, 

 he at once jumped to the conclusion that 

 this bone must be the missing quadrate. 

 Now, the fact that cartilage is unknown in 

 this region would at once negative any such 

 conclusion, while the further fact that the 

 skull in question was that of an imbecile 

 and the additional bone occurred on one 

 side only, is certainly suggestive. E'o his- 

 tory of the case was given, but it is not be- 

 yond the bounds of possibility that an in- 

 jury to the head may, at the same time, 

 have caused the imbecility and have pro- 

 duced the supernumerary bone, upon which, 

 as a very slender basis, a considerable super- 

 structure of speculation has been built. 



There is one series of facts which may 

 possibly lead to an explanation of this 

 change in point of articulation. In certain 

 sharks there occur labial cartilages which 

 lie outside of the jaws and perfectly free 

 from them. Now, the cartilage mentioned 

 above as occurring in connection with the 

 dentary bone of mammals, occupies the 

 position of one of the lower of these labial 

 cartilages — Parker has, indeed, identified 



