COPE 



arrangement, especially of the contents of the class Agnatha, 

 must be regarded as largely provisional. 



The ossification of the skeleton of the Vertebrata has 

 developed first on the exterior of the head and body and in 

 the sheath of the chorda dorsalis, and has then penetrated 

 inwards. The limbs have preceded in time the arches 

 (scapular and pelvic) to which they are, in the higher 

 forms, attached. Hence we find in such genera as Cepha- 

 laspis and Bothriolepis pectoral limbs without a scapular 

 arch, but with merely dermal ossifications to which they are 

 attached. This is parallel to the general absence of most of 

 the pelvic arch in fishes. The limbs themselves are sup- 

 posed to be radial ossifications in primitive longitudinal 

 folds of the body integument, some of which remain in 

 large part, as the dorsal fin of various fishes ; while more 

 frequently but few of the radii remain, as in the limbs of 

 most Vertebrata. (Fig. 1.) 



The use of this syllabus presupposes a knowledge of the 

 rudiments of vertebrate anatomy. The subject is presented 

 in zoological order, but tables are given, in which the tax- 

 onomic divisions are represented in their stratigraphic 

 position and succession. 



Fig. ]. — Diagrammatic representation of primitive and derivative types of lateral 

 and median fins. A^ primitive condition, fins continuous; B, derivative condition, 

 flns distinct and specialized. D, dorsal fin; BrF, pectoral; BF, ventral; AF, anal; 

 8F, caudal; RF, dorsal; FF, second dorsal fin. From Wiederslieim. 



