August 9, 1901.] 



SCIENCE. 



199 



Here embryology comes in to assist. The 

 development of these bones has been fol- 

 lowed by many, and it is a rather sig- 

 nificant fact that while the embryolo- 

 gists are in substantial agreement in their 

 interpretations, their opinions are at vari- 

 ance with those of the students who 

 have attacked the problem from the stand- 



FiG. C. Diagram of the Ear Eegion in a Mammal. 

 s, stapes ; i, incus ; m, malleus ; ct, chorda tympani 

 nerve. 



point of adult structure. Now, since the 

 embryologists have the wider view, the 

 larger basis of facts at command, on a priori 

 grounds their conclusions should be given 

 the greater weight. Embryology plus com- 

 parative anatomy certainly forms a better 

 basis for conclusions than comparative an- 

 atomy alone. 



In the embryonic mammal, before the ap- 

 pearance of cartilage, a strand of denser 

 mesenchyme extends from the point where 

 the anlage of the stapes can be recognized 

 into the lower jaw. Position and relation- 

 ships show that this strand is the first ap- 

 pearance of the mandibular arch. With 

 the formation of cartilage this arch becomes 

 divided into a proximal portion, which can 

 be traced, step by step, until it develops into 

 the incus and a more distal portion, which 

 is as clearly Meckel's cartilage, extend- 

 ing into the lower jaw. This incus soon 

 develops an articular surface for connection 

 with the stapes, while a second set of sur- 



faces is found between the incus and the 

 proximal end of the Meckelian cartilage. 

 The incudal surface of this last is convex, 

 while the corresponding articular surface on 

 Meckel's cartilage is concave. It follows 

 from these facts of development and struc- 

 ture, as well as from others which cannot 

 be detailed here, that the incus fulfills, in 

 the embryonic stages, every condition de- 

 manded for the quadrate, while the great 

 size of these elements in the early condition 

 can only be interpreted as indicative of 

 some function in their ancestral history dif- 

 ferent from that of a sound- conducting ap- 

 paratus. Again, it is a matter of no little 

 importance in what will follow, that this 

 quadrate articulates with the stapes just as 

 in many urodele amphibia, while such re- 

 lationships are unknown in any reptile, 

 living 01" fossil. In the third place, this 

 incus for a time articulates directly with 

 the skull, just as does the quadrate in the 

 lower forms, a condition not easily explic- 

 able upon any other view than that regard- 

 ing this as the quadrate. 



Fig. D. Diagram of the Ear and Lower Jaw in 

 the Pig. an, angulare ; d, dentary ; i, incus ; j, 

 jugal ; I, cartilage of articular region of lower jaw ; 

 m, malleus ; mk, Meckelian cartilage ; s, stapes ; sp, 

 splenial ; z, zygomatic process of temporal — the letter 

 lies just in front of the glenoid fossa. 



The malleus is largely formed by the 

 ossification of the proximal end of Meckel's 

 cartilage, and this fact, together with every 



