THE ENDOSKELETON: GIRDLES, THE STERNUM, AND APPENDAGES 80 



the trunk. The median ventral portion between the bases of the two fins is 

 called the coracoid bar; the long processes extending dorsally beyond the articula- 

 tions of the fins are the scapular processes; the ends of the scapular processes 

 commonly consist of separate pieces, the suprascapular cartilages. The pectoral 

 fins are similar to the pelvic. They are supported at their bases by several series 

 of cartilaginous fin rays and externally by dermal fin rays. The cartilaginous 

 fin rays consist of a proximal row of enlarged basals and several distal rows of 



posttemporal 



. supraclavicle 



upper postclavicle 



clavicle mesopterygial cartilage 



radials 



FIG. 30. Pectoral girdle of a crossopterygian fish, Polypterns, to show the large number of mem- 

 brane bones occurring in the pectoral girdle of teleostome fishes. Viewed from the inside (dorsal view) 

 Membrane bones, blank; cartilage bones, close stippling; cartilage, open stippling. Note also the 

 arrangement of the basals and radials in the "stalk" of the fin, the external appearance of which is 

 shown in Figure i. (After Goodrich in Part IX of Lankester's Treatise on Zoology, courtesy of the 

 Macmillan Company.) 



smaller radials. There are generally three basals : an inner one, the largest, the 

 melapterygium; a middle one, the mesopterygium; and an outer one, the prop- 

 terygium. There is no trace of a sternum as such, but the median ventral 

 portion of the coracoid bar may be regarded as the primordium of the sternum 

 on the basis of the theory of the origin of the sternum presented at the beginning 

 of this section (see Fig. 26, p. 85). Draw the pectoral girdle and one pectoral fin. 

 4. The pectoral girdle and fore limb of urodeles. -In urodeles the girdle is 

 still in a primitive condition. Necturus or Cryptobranchus may be studied. On 

 the ventral side the girdle forms paired, flat cartilaginous plates, which may be 

 designated the coracoid plates. The anterior part of these plates may be 

 regarded as a procoracoid region; this projects forward in Necturus as an 



