98 H. H. NEWMAN. 



ments and additions in the mid-neural and costal regions, there is 

 not a single case of sympathetic plate abnormality. 



Another strong case in favor of the entire independence of 

 these structures is furnished by examples of vertebral distortions. 

 A paper by Wandolleck (1904) entitled "A Hump-Backed 

 Tortoise," describes a specimen of Tcstudo Grceca in which the 

 neural and costal plates were in utter confusion, due to lateral 

 curvature of the spine. Yet the number and arrangement of the 

 scutes was perfectly normal. Another case in point is that of a 

 deformed embryo in my possession that has ten ribs on one side 

 and the number of costal scutes is perfectly normal (Fig. 56). 



Further evidence for the independence of neural and costal 

 scutes and plates is derived from the fact that certain land tor- 

 toises undergo striking modifications of plates in order to form a 

 dome-shaped shell of great strength. The costal plates become, 

 dovetailed one into the other and are decidedly wedge-shaped. 

 This condition is not followed in any respect by the scutes, which 

 retain their typical form and arrangement. A. Bienz ('94) de- 

 scribes this condition in Dennatcmys inavit, and shows that the 

 form and the arrangement of the plates conform with the most 

 approved architectural principles. 



The origin of the bony plates of the plastron has been thor- 

 oughly worked out and in each case a plate is to be interpreted 

 as a modification of preexisting bony structures clavicle, ster- 

 num or abdominal ribs. If such structures as these have been 

 transformed into large, flat, bony plates without any fusion of 

 fascia bones or any outside factors of any sort, why is it neces- 

 sary to explain the costal and neural plates as other than mere 

 modifications of the preexisting ribs and neural spines ? 



6. Correlation in Scute Abnormalities. 



Two tendencies may be noted in this connection : 



1. Scutes of the same horizontal row have a tendency to recur 

 together (see Figs. 3, 5, 6, 7, 8, 9, 10, 12, 13, 14, 20, 31, 33 

 35,40). A i o neural most frequently is accompanied by a 10 

 costal, etc. 



2. In asymmetrical abnormalities the tendency is for super- 

 numerary neurals, costals and marginals to occur on the same 

 side (see Figs. 3, 5, 7, 8, 9, 10, 12, 13, 14, 31, 35, 40). 



