254 



THOMAS DWIGHT ON 



Class II. 



(21, 5G1, 361, X, G-22, A-175, 2.) 



This class includes spines in which there is an approach, more or less near, to 25 

 perfect praesacral vertebrae. In the first the 2oth vertebra is almost a sacral one, in the 

 last it is almost a piu'c himbar. They are arranged to mark the steps of this progression 

 as regularly as possible. In every one of this class the 2(jtli is the rertehra fulcralis, i. e., 

 the one ha\dng the largest surface articulating with the ilium. Also in ever}' case there 

 is more or less of a disc lietween the 25th and the 26th. As the degree of sacralization 

 of the 25th has been made the l)asis of arrangement of this class, it has been necessary to 

 disregard the numljer of ribs, and even the synostosis of atlas and occiput. 



21. Cat. 9379-7. 



Female, white, aet. 10. C. 7, T. 13, L. 5, S. 4. (C. 4?). 



There is some difficulty in decitUng the limits of this sacrum ; 

 but in view of the facts that the 26th is clearly the _/V/cr«/i.s-, and 

 that the 2(lth is a thoracic at least (m one side, I have put the 

 25tli in the lumbar region though it superficially resembles a 

 sacral vertebra very strongly, and there are only 4 sacrals below 

 it. The coccyx is hard to count, probably containing 4 pieces. 



There is nothing worthy of note above the 20th vertebra, 

 which has a distinct rib on the riy'ht, 3.7 cm. hmo-, witli a head, 

 and clearly in line with the others. On the left the costal ele- 

 nu'ut has been lost in the preparation. It was almost wholly 

 cartilaginous, from 1 to 2 cm. long. No certain facet for a head 

 can be found. The change in the articular processes is ill 

 marked, apparently occurring, on the right, below the 19th, and 

 on the left, a vertebra lower. The spread of the transverse proc- 

 esses of the loins is aliout the same (excepting the 25th) and 

 is a little greater in the first. The 25th has an ill-marked prom- 

 ontory below it. It forms a part of the convexity of the loins, 

 and there is the slightest suspicion of a promontory alK)ve it. 

 This want of i very definite promontory is characteristic of the 



