258 



AUDITOEY OSSICLES 



form a suspensory apparatus for the mandible, are in higher vertebrates, as 

 it were, annexed by the organ of hearing to provide an apparatus for sound - 

 transmission. 



Formation of the auditory ossicles. The development of the auditory 

 ossicles in the human subject has in recent years been investigated again in great 



incus 



interhyal 

 cartilage 



handle of malleus 

 chorda tympani 



cartilage of Reichert 



FIG. 311. KECONSTBUCTION OF THE PBOXIMAL ENDS or THE FIRST AND SECOND BRANCHIAL ARCHES 



OF A HUMAN EMBRYO OF 16 MM. LONG ; LEFT SIDE, INNER ASPECT. (After Broman.) 



V., fifth nerve ; VII., facial nerve. 



detail by Broman, and also incidentally by Hammar. The following account sum- 

 marises the chief points of Broman' s researches. They confirm in the main the 

 views first enunciated by Reichert in 1837. l In the middle of the second month 

 the rudiments of the ossicles appear as chondroblast thickenings in a common 



head of malleus 



tympanic ring 



incus 



facial nerve 

 I ear-capsule 



chorda tympani 



handle of malleus 



cartilage of Reichert 

 facial nerve 



FIG. 312. THE SAME MODEL AS SHOWN IN FIG. 811, SEEN FROM THE OUTEB SIDE. 



blastema outside the first visceral pouch. This blastema is divided in the 

 mandibular arch by the trigeminal nerve, and in the hyoid arch by the facial nerve, 

 into mesial and lateral portions. In the mandibular arch the proximal part of the 

 lateral mass becomes the rudiment of the incus, while the corresponding part in the 

 hyoid arch represents the later ohyal cartilage. The distal portions of the lateral 



1 Meckel discovered the cartilage which bears his name in the human embryo in 1820. He observed 

 its continuity with the malleus, but the interpretation of the facts was due to Reichert. 



