THE ENDOSKELETON 161 



stylo-hyal, and tympano-hyal, the last closely associated with 

 the external opening of the ear. In man and the higher apes 

 the two latter are fused with the skull to form the ff styloid- 

 process of the temporal bone," and this is connected with 

 the cerato-hyal (=" lesser or anterior cornua ") by the stylo- 

 hyoid ligament , which replaces the missing epi-hyal. Oc- 

 casionally a rudiment of this latter bone is found in the middle 

 of the ligament. 



A recently described and very singular metamorphosis of 

 a portion of a visceral arch is that by which in mammals the 

 outer end of the 2nd or hyoid arch, naturally located near the 

 external opening of the ear, segments off and becomes trans- 

 formed into the cartilage of the external ear-flap, the auricula 

 or pinna, which in the various Orders responds readily to the 

 varied environments of different mammals and exhibits a 

 great range of variation in shape and size. 



Of what a series of changes and unexpected metamorpho- 

 ses has the visceral skeleton shown itself capable, and what 

 vicissitudes have the several elements experienced ! Beginning 

 as a set of similar arches, regulating the opening and closing 

 of gill-slits, they become jaws, vocal organs, supports for the 

 tongue, suspensory pieces for the mandible, tympanic ossicles 

 and flapping external ears. Indeed, a well-recognized, though 

 not generally accepted, theory derives from them also the 

 skeleton of the free limbs, including the shoulder and hip 

 girdles, and even the long bones of the limbs and the numer- 

 ous smaller pieces in carpus and tarsus and in the digits. But 

 even without this latter theory, which appears untenable, the 

 subject presents a remarkable history of repeated change 

 of function, of the adaptation of old material to new 

 purposes, of the dethronement of the old systems and 

 the employment of their organs for the development of 

 the new; we see here Nature constantly exploring new 

 environments, and then adapting function to environment, and 

 material to function, constantly making over old organs in 

 obedience to mechanical laws and never originating or creating 

 new ones de novo. The results are thus often imperfect and 



