302 THOMAS DWIGHT ON 



Of the deductions that may be made from these specimens, some are of merely 

 morphological interest, while others are far-reaching. It is not possible to separate the 

 two groups completely. 



Terminal Vertebrae and Those at the Ends of the Different Regions of the Spine. — 

 It seems beyond question that certain vertebrae are capable of having the characteristics 

 of those above or below them in numerical order. The last cocc^'geal may be just the 

 same to all appearance, though its number from the atlas may differ by several places. 

 The last sacral and 1st coccygeal are absolutely vmcertain. As the vagaries of the 24th, 

 25th, 26th, and even the 27th, any one of which may be the fidcralis, are at the basis of the 

 classification adopted in this paper, they need not be discussed here, except in so far as 

 the condition of a given vertebra affects that of others, as foi- instance the effect 

 of a certain vertebra being the fidcralis on the two vertebrae above it and on the 

 sacrum as a whole. It is rather surprising that no effort has ever been made to decide 

 whether sacra could be distinguished one from another according to the particular verte- 

 bra that happens to be the fidcralis. From this series it would seem that there are cer- 

 tain peculiarities which in most cases would enable us at the very least to separate the 

 sacra in which the 24tli is the fidcralis, and those in which it is strongly sacralized, from 

 those in which the 25th or the 26th is the fidcralis. On the other hand slight sacraliza- 

 tion of the 24th and 25th may be very similar. Wliile it is likely that a larger series 

 would show more instances of difficult diasrnosis, I think it would confirm the deductions 

 from the present one, which are as follows : 



Distinctions between Spines vnth Sacra of Different Nnmerlcal Composition. — 



I. When the 26th is the fidcralis and the 25tli more or less sacralized, the prom- 

 ontory is perfectly evidently above the former, and there is no secondarj' promontory. 

 The 25th, apart from its sacralization, is a good last lumbar, the disc below it, though 

 much diminished, is always present, and the 24th is always a penultimate. (The spine 

 of a child of ten (spine 21) is the only exception to this rule. The promontory is not 

 over-evident, nor is the possibility of a secondary one to be denied ; but this, it is to be 

 remembered, is a characteristic of the pelvis of early childhood. Spine X is very dif- 

 ferent on the two sides, and I hesitate to affirm that, if looked at from the right side only, 

 there might not be doubt about the position of the promontory.) 



II. When the 25th is qviite free, the promontory is always unmistakably below it. 

 The 25th and 24th are generally pretty typical ultimates and penultimates. 



III. When the 24th is sacralized more or less, but is not the fidcralis, tlie position of 

 the promontory is not clear, and sometimes very doubtful, being either above or below 

 the 24th or being double. There is little or no remnant of a disc below the 24th. The 



