70 



G. -T. de Fej ervary: 



German authors, and the cartilaginously preformed ,,cartilage 

 bones", known under the name of Ersatzknochen" or Knorpel- 

 knochen" in the German anatomical Literature. 



The former ones, which are designated as ,,Allostoses", • 

 must be looked upon as phylogenetically derived from an ancestral 

 exoskeleton, whilst the latter ones — the ,,Autostoses" — 

 constitute the pfimary Clements of the endoskeleton, i. e. 

 the primordial or chondroskeleton. Phylogeny has teached 

 US that the first ossifications are represented by the Clements 

 originated from the ancestral exoskeleton, whilst the ossi- 

 fication of the different parts of the undoubtedly more ancient 

 cartilaginous (primordial) skeleton occurred but in a somewhat 

 later phase of Vertebrate Evolution. 



It cannot be my Intention to enter into detail s concerning 

 the autostotic and allostotic mode of development of the various 

 skeletal and especially cranial Clements, nor to deal with the 

 principles of their often so difficult homologization in the different 

 Classes and Orders, a problem the, difficulty of which may 

 be still increased by cases of fusion or by complicated 

 coenogenetical phenomena. I shall merely confine myself to the 

 Statement that, as regards the development of dermal and chon- 

 dral ossifications, the evidence of three types has been established, 

 which are represented by: the cartilage bones, the dermal bones^j 

 including s. lat. the odontogenous bones (,, Zahnknochen") as 

 well, and the socalled mixed bones.^) 



It is but the secord of the three mentioned types which shall 

 be here discussed. 



As stated above, the dermal (or ,,membrane") bones, which, 

 nowadays, represent integrant components of the Vertebrate 

 skull (i. e. of the endoskeleton), are the off spring of ancient 

 exoskeletal Clements. I will designate this ancestral exo- 

 skeleton as the primary exoskeleton, in Opposition to the secondary 

 exoskeleton occurring in phylogenetically ycunger forms, i. e. in 

 some Fish es and in various representants of the Classes of Ba- 

 trachians, Reptiles and Mammals.^) 



In the Fishes, which present the greatest complexity with 

 lespect to their osteological features, the distinction between 

 primary and secondary exoskeletal Clements constitutes a very 

 difficult problem. In a very large number the dermal bones of 



^) The term ,,membrane" bone, by which the Deckknochen." of the 

 skull are generally designated, though corresponding to their embryological 

 development, is rather inadmissible from a phylogenetical point ot 

 view. I prefer to use, therefore, the expression ,,dermal bone". 



^) The ossifications of ligaments and miiscles will not be 

 here considered. 



^) Birds are devoid of exoskeletal ossifications; in this Class it is but 

 the sclerotical ring which might be looked upon as constituting an exo- 

 skeletal" Clement; at present, however, this special foiTnation shall be left 

 out of consideration. 



