DEVELOPMENT OF SKULL: REICHERT 145 



the first process this rod shows three segments, of which the 

 first lies inside that portion of the process which is parallel 

 with the head. This upper segment forms the foundation 

 for the bones of the upper jaw. The lowest segment of the 

 cartilaginous rod becomes Meckel's cartilage, and on the 

 outer side of this the bones of the lower jaw are formed. 

 The middle segment becomes in mammals the incus (one of 

 the ear-ossicles), and in birds the quadrate. Meckel's cartilage, 

 which was discovered by Meckel l in fish, amphibians and 

 birds, is a long strip of cartilage which runs from the ear- 

 ossicle known as the hammer in mammals, 2 to the inside of 

 the mandible. Reichert shows how this relation comes 



FlG. 9. Meckel's Cartilage and Ear-ossicles in Embryo 

 of Pig. (After Reichert.) 



a. Mandible. h. Hammer. k. Incus. 



g. Meckel's cartilage. i. Handle of Hammer. n. Stapes. 



about. The hammer, according to his observations on the 

 embryo of the pig, is simply the proximal end of Meckel's 

 cartilage, which later becomes separated off from the long- 

 distal portion (see Fig. 9). The third ear-ossicle of mammals, 

 the stapes, comes not from the first arch but from the second. 

 The cartilaginous rod of the second arch segments like the 

 first into three pieces. Of these the uppermost disappears, 

 the middle one, which lies close up to the labyrinth of the ear, 

 becomes the stapes, and the lowest becomes the anterior 



1 Handbuch d. menschl. Anatomic, iv., p. 47. 



2 This was shown by Serres (Ann. Set. nat., xi., p. 54 f.n., 1827), who 

 found in a human embryo a long cartilaginous piece extending from 

 the ear-ossicles to the inside of the lower jaw, and suggested that it 

 was the foundation of the permanent mandible. 



