THE SKELETON OF THE VERTEBRATE HEAD. 191 



form together a well-marked haemal arch, developed in the 

 first post-stomal visceral lamina of the embryo. From what 

 has already been stated regarding the sclerous elements which 

 result from the development of this visceral lamina in the 

 other Vertebrata, Professor Owen's view of the tympanic 

 system of the osseous fish, as the teleologically-divided homo- 

 logue of the quadrate bone of the bird, and tympanic bone of 

 the reptile, would appear to require additional evidence. We 

 are not yet in possession of materials for a rigorous determina- 

 tion ; but it appears extremely probable that the tympanic 

 bones of the osseous fish are morphological, as well as teleo- 

 logical elements. If the articular piece of the lower jaw be 

 assumed as the malleal portion of the persistent cartilage of 

 Meckel, the hypo-tympanic occupies the position of the in- 

 cudal element, connected, as usual, with the pterygoid. The 

 epi-tympanic is in the position of the proper tympanic element 

 of the mammal, while the pre-tympanic, in its relations to the 

 hypo-tympanic and pterygoid, closely resembles the quadrate- 

 jugal or squamosal. 



The opercular bones form on each side of the mandibular 

 arch a series of actinapophyseal elements, which, from the 

 view already taken of such elements, would appear to be pos- 

 terior, as the quadrat e-jugal or squamosal is anterior in rela- 

 tion to the sclerotome. With regard to any traces of these 

 opercular or actinapophyseal elements in the mandibular 

 haemal arch of the higher Yertebrata, I must agree with Carus 

 in considering the cartilages of the external ear in the Mam- 

 malia as homologous with them. The objection of Eathke to 

 this determination of Carus that the cartilage of the concha 

 is attached to the tympanic bone so as to be situated at the 

 back of the auditory foramen that is, at the posterior margins 

 of the first visceral cleft appears to me to be met by taking 

 into account the peculiar curved form which the tympanic ele- 

 ment assumes in passing from before backwards across the cleft. 



