Royal Institution. ^07 



lating with the process representing the coalesced postfrontal. In 

 return, we find the hyoidean arch resuming its normal connexions in 

 many mammalia, the stylo-hyal element being directly articulated to 

 the mastoid : in man the large petrosal capsule intervenes, and con- 

 tracts that anchylosis with the proximal or pleurapophysial element 

 of the hyoid arch, which has led to the description of the stylohyal 

 as a process of the temporal bone, in works on human anatomy. 



In fishes, the tympanic, which is the true pleurapophysis of the 

 mandibular arch, always articulates with the postfrontal, besides its 

 accessory joint with the mastoid. The maxillary arch is articulated 

 by its pleurapophysis, the palatine bone, with the centrum and neu- 

 rapophysis (vomer and prefontal) of the nasal vertebra. This is the 

 normal and constant point of suspension of the maxillary arch ; other 

 accessory attachments to ensure its fixation and strength are succes- 

 sively superinduced upon this primary and essential one. Through 

 this knowledge of the general homology of the palatine, an insight 

 was gained into its singular disposition in man, creeping up, as it 

 were, into the orbit, to touch the pars plana of the sethmoid ; thi^ 

 secret afiinity with the modified neurapophysis of the nasal vertebra 

 becomes intelligible by a recognition of its relations to the general 

 type of the vertebrate skeleton, by its determination as the rib or 

 pleurapophysis of the nasal vertebra, and therefore retaining, as such, 

 more or less of its essential connexion with the centrum (vomer) and 

 neurapophyses (sethmoid or prefrontal) of the nasal vertebra through- 

 out the vertebrate series. 



The tympano-mandibular and the hyoidean arches had both been 

 recognized as resembling ribs. A like homology of the scapula had 

 early been detected by Oken ; but its relation to the skull or occiput 

 had been masked, and had escaped previous notice, by its displace- 

 ment from its natural or typical connexions in all the air-breathing 

 vertebrata. 



The enunciation of these correspondences has sometimes been re- 

 ceived by anatomists conversant with one particular modification of 

 the general type, with as little favour as those of the " cannon-bone" 

 to the metacarpus, of the " great and small pastern" and the " cofiin- 

 bones" to the digital phalanges of the human hand, may be supposed 

 to have been by the earlier veterinarians. 



Prof. Owen adduced instances of the displacement of diflferent 

 vertebral elements to subserve special exigencies, as that of the neu- 

 rapophyses in the bird's sacrum, and that of the ribs in the human 

 thorax, in which there could be, and had been, no question as to the 

 reference of such displaced parts severally to their proper vertebral 

 segments. The displacement of the scapular arch from the occiput 

 was a modification of precisely the same kind, and dift'ered only in 

 degree. In the crocodile every cervical as well as every dorsal ver- 

 tebra had its ribs ; and in the immature animal the same elements 

 existed, as distinct parts, in the lumbar, sacral, and in several caudal 

 vertebrae. The occipital vertebra would be represented only by its 

 "centrum" and "neural arch," unless the loose and obviously dis- 

 placed scapulo-coracoid arch were recognized as ita pleurapophysial 



