10 PROCEEDINGS OF THE NATIONAL MUSEUM vol.73 



It must be remembered that we are dealing with structures which, 

 as the writer maintains, became useless thousands of generations ago 

 and ceased to be reproduced by the great majority of turtles. It is 

 not strange, therefore, that they appear in the matamata irregularly 

 and in some cases not at all. Doctor Noble must recall what happens 

 in the case of the canine teeth of mares and of the first premolars of 

 horses in general, not to mention other similar examples. 



Doctor Noble appears to suggest the attacks of parasites on these 

 captive matamatas, but he does not pursue the subject. The life 

 history of such a parasite would be interesting, if it exists. Doctor 

 Noble, however, finally concludes that the ossicles in question seem to 

 be bony deposits over injuries received either during captivity or 

 rarely in nature. He ought to have told us whether he has observed 

 similar bony deposits beneath the uninjured epidermal scutes of 

 snapping turtles and terrapins kept in confinement. 



9. PROCTOR'S RESULTS FROM THE STUDY OF TESTUDO 



Mention has just been made of the work of Joan B. Proctor on 

 the anatomy of Testudo. In her effort to determine whether the 

 costal plates are simply expansions of the ribs or originate inde- 

 pendently of them that author examined the recently hatched young. 

 She found that the embryonic costal plate was in contact with the 

 rib; also that the rib was undergoing degeneration at a time when 

 the costal plate was growing vigorously. She concluded, therefore, 

 that the plate was not derived from the rib. She was led to consider 

 also the relation of the developing horny scutes to these costal plates 

 and in doing so she hit upon a condition which, then unknown to 

 her, had been described by Richard Owen. In the young tortoise the 

 horny scutes are already present and relatively large. Inasmuch 

 as the vertebral scutes alternate with the costal scutes, there is along 

 each side of the dorsal region a zigzag series of points, from each of 

 which radiate the edges of three scutes. The author cited found that 

 a costal plate developed immediately undei' each of these triradiate 

 structures and that the forms of these plates in their early stages of 

 development were in strict correlation with the sutures between the 

 superincumbent epidermal shields. 



Now, with few exceptions, and these probably of secondary 

 origin, the plates and scales of dermal bone in reptiles underlie and 

 support the horny scutes, and the two structures agree more or less 

 exactly in form and size. If the explanation proposed by Proctor 

 is correct the costal plates take their origin at the intersections of 

 the borders of three scutes and these scutes determine the early forms 

 of the plates. The present writer believes that these conclusions are 

 erroneous. The presence of the bones beneath the borders of the 



