318 MR. W. K. PARKER ON THE OSTEOLOGY OF BAL.ENICEPS REX. 



hyal is nearly ossified in the Chick ; but the small triangular glosso-hyal, the short 

 terete divaricating cerato-hyals, the basi- and uro-hyals, as well as the distal thyro-hyal, 

 are all entirely cartilaginous. In the Pigeon, at the time of hatching, we have the same 

 state of things. In many birds the glosso-hyal, and the tips of the uro-hyals and thyro- 

 hyals (distal pieces) remain cartilaginous. 



Sclerotic Bones and Columella. 

 The sclerotals form a ring H inch across ; their largest pieces are about a quarter of 

 an inch wide : they are well-ossified. The ' columella ' has not been preserved in this 

 specimen ; and the complex structures of the internal ear are formed principally by the 

 petrosal, yet impinge upon and are partly formed by the surrounding bones, e. g. the 

 epiotic and the mastoid portion of the ex-occipital. The basi-occipital and basi-sphenoid 

 also contribute some part of their substance to the formation of the hard parts of this 

 sense-organ. 



Recapitulation of the Cranial 'Elements' 



We will retrace our steps a little, and look again at the constituent parts of the skull 

 and face. 



It is very convenient to consider the skull as a ' sys-sclerotome,' divided into a cer- 

 tain number of ' sclerotomes.' This method is more convenient than safe ; but we will, 

 as much as possible, avoid theorizing ; yet we cannot, we think, go very far wrong if 

 we consider what amount of segmentation is to be seen along the base of the most 

 perfect skulls, e. g. those of the Mammalia. 



In these creatures we have, from behind forwards, four basal parts or ' centra,' viz. 

 the basi-occipital, the basi-sphenoid, the pre-sphenoid, and the mesial portion of the 

 ethmoid ; this latter bony mass having appended to it in front a large vertical cartila- 

 ginous apophysis, the ethmo-vomerine cartilage, whilst the thin cortical ' vomer ' is 

 related to it (indirectly) below. That great modern anatomist whose mind is most 

 opulent in knowledge of these structures. Professor Owen, has only been able to make 

 out four ' vertebrae ' in the skull of the Vertebrata. Whilst we use Professor Owen's 

 ' homological ' terms for the cranial 'elements,' we still consider them only the 'ana- 

 logues,' and not the true ' homologues,' of the pieces that go to make up a corporal ver- 

 tebra. Moreover we shall find that the lateral and upper pieces do not correspond in 

 number to the basal, and that the same bone may be a ' neurapophysis,' a ' diapophy- 

 sis,' or a ' sense-capsule.' Whatever we may call this confusing abundance of upper 

 and lateral pieces, whether segmentation, ' vegetative or irrelative repetition,' or ' inter- 

 calation of splanchnic bones ' or ' sense-capsules,' we are still under the necessity of 

 referring back to the unsegmented primary skull of the embryo ; and any attempt to 

 explain the nature of the skull which shall not be based upon a very extended ' embryo- 

 logy ' will turn out to be mere waste of time. 



