Sentence:  Outlines of the chief developments of the dermoskeleton, in different vertebrates, which are usually more or less ossified, are added to the endoskeletal <WSD>archetype</WSD>: as, "e.g." the median horn supported by the nasal spine ... in the rhinoceros; ... 
Meaning of the word marked with <WSD> tags:  An original model of which all other similar concepts, objects, or persons are merely copied, derivative, emulated, or patterned; a prototype. (from mid 16th c.)