THE ENDOSKELETON 



149 



ime very near being, this portion of the history might have 

 ;n deciphered from the embryological records, since even in 

 ic mammals the primordial skull develops from its primitive 

 ilements, the cartilage bones appear as centers of ossification 

 it, and the dermal bones, never preformed in cartilage, 

 ippear as subcutaneous ossifications in the connective tissue. 



A 



FIG. 39. Two views of the skull of Cryptobranchus allegheniensis, a 

 primitive salamander, a little higher than Necturus. 



(A) Dorsal. (B) Ventral. 



DERMAL BONES: pm, premaxillary; mx, maxillary; n, nasal; f, frontal; pr. f t 

 pre-frontal; p, parietal; sq, squamosal; pt, pterygoid; vp, vomero-palatine; pb, para- 

 basal. 



CARTILAGE BONES: os, orbitosphenoid; q, quadrate; ex. o, exoccipital op, operculum, 



OTHER PARTS: col, columella; nas, nasal capsule; ec, eye capsule; ot, otic cap- 

 sule. 



In both figures the dermal bones have been retained on the right side of the 

 skull and removed on the left. 



In that case, however, we could hardly have obtained an idea 

 of the appearance of the adult ganoids, since embryology, with 

 its distortion of the facts through an early assumption of. the 

 proportions of the perfected animal, is an unsafe guide upon 

 which to base more than very general conclusions. Had the 

 ganoids been lost we would have believed in a general way 

 in the former existence of fish-like forms in which the dermal 

 bones were still in the form of an exoskeletal armature, but 

 their exact appearance and relationship would have given rise 



