22 THE SALAMANDER 



Any description of a Urodele skull falls naturally into two clearly 

 defined sections, first, the primordial skeleton, comprising both 

 cartilage and endochondrial ossifications, and second the investing 

 bones. 



2. The Primordial Skeleton. 



The primary cranium of the Salamander is in many respects 

 less developed than either the Frog or Dog-fish, and forms an excel- 

 lent 'ideal' type. Both the roof and the floor of the brain-case 

 are almost uncovered, the bridges between the right and left sides 

 being entirely confined to the regions of the sense capsules. Thus 

 the chondro-cranium consists roughly of a pair of olfactory capsules 

 and a pair of otic capsules connected together by two longi- 

 tudinal bars of partially ossified cartilage, while with the otic 

 capsules are associated the occipital ring posteriorly, and the 

 palato-quadrate laterally. As a protection to the eye a sclerotic 

 ring is developed around that organ in the larva, but disappears 

 during metamorphosis. Four regions of the primary skull are thus 

 distinguishable. 



{a) The Ethmoidal Region consisting of the nasal capsules and 

 their connectives. The accurate and detailed study of this region is 

 practically impossible except by one or other of the reconstruction 

 methods ; any attempt to raise the investing bones being almost sure to 

 damage the thin cartilages lying beneath. Bremer (1924)1 adopted 

 the wax-plate method of reconstruction and studied the development 

 of the nasal capsules of Salamandra very thoroughly by this means. 

 The following description of the ethmoidal region is based largely on 

 his account. 



This portion of the primary skeleton forms about 30 per cent, of 

 the total length of the skull. The walls of the nasal capsules are by 

 no means complete, but are perforated by several large fenestrae as 

 follows : 



(i) The fenestra basalis nasi (fen.b.nas.) in the floor is covered 

 ventrally by the pre-vomer and, to a slight extent, by the pars pala- 

 tina of the maxillary. The internal nares (nar.i.) or choanae enter the 

 posterior portion of this fenestra. It is bounded posteriorly by the 

 cartilago antorbitalis (c.a.or.), laterally by the cartilago ectochoanalis 

 (c.ec.ch.), anteriorly by the cornu trabeculae, and mesially by the 



^ Bremer's account has not been published under his name but is incorporated in 

 Stadtmiiller's (1924) paper on the skull. By the kindness of the Librarian of the Uni- 

 versity of Gottingen the author has been enabled to consult the original typescript of 

 Bremer's thesis. 



