306 THOMAS DWIGHT ON 



believe that these two types are distinct, and represent what is commonly seen at differ- 

 ent levels of the spine, I would not undertake to say that either may not be found some 

 time at the level of the other. In this series there is one case (208) of the fusion of the 

 three upper thoracic ril)s. 



I shall return to the condition of the spine as a whole in cases of cer\acal and de- 

 fective 1st thoracic ribs. 



Fusion of Atlas and Occiput. — There is no reason why this occurrence should not 

 have the same weight in the numerical variations of the spine as fusion at other points. 

 There are several specimens in this series which have been sufficiently described. Is this 

 condition a return to the past (if so, to what past ?) , or a step towards the future ? 



The Fusion of the Axis and 3d Vertebra. — Fusion occurs occasionally as a patho- 

 logical process, usually of advancing years, in any part of the spine. There are also 

 certain places where it exceptionally occurs more or less frequently in the course of 

 development, as between atlas and occiput, last lumbar and 1st sacral, last sacral and 1st 

 coccygeal. There is another place whicli seems one of predilection, namely between the 

 axis and the vertebra below it. Leboucq ('96-'98) has described two cases, both with 

 imperfect ribs on the 8th vertebra, in wliich he thinks there is a partial reduplication 

 of the axis, inasmuch as in certain fissures on the antei'ior surface he sees a repetition of 

 the superior articular siu'faces of the axis placed ventrally to the intervertebral foramina. 

 This is the case only in his first specimen. In the second the fusion is more thorough, 

 and the lines of separation lost. In the latter, moreover, there is an intimate fusion of 

 the arches. I am somewhat inclined to question tlie accuracy of the interpretation 

 because these fissures on the anterior surface, judging from Leboucq's drawing, do not 

 correspond with the direction of the superior ai'ticular surfaces of the atlas. These 

 latter slant from the middle downward and outward, while the fissures are inclined 

 upward and outward. Moreover, in the first of my detached specimens (4767) there 

 is on the right of the anterior surface a horizontal slit below the superior articular 

 process of the atlas that looks at first like a repetition of it, but which, as is shown by 

 the median section, is certainly in the axis and not beneath it. Neither in Leboucq's 

 second case nor in any of my series is there another instance of such an appearance. In 

 this series there are two cases of fusion of these vertebrae without any history of the rest 

 of the column. In the complete spines there are two other cases, one certain and one 

 perhaps somewhat doubtful. The former (204) has the bodies fused and the laminae on 

 one side so intimately mixed as to appear as one. In 297 (20 praesacrals) the bodies 

 are fused but apparently not mixed (if I may use the expression) , but there is a t\ision in 

 the arch that points to a congenital condition. Leboucq tliinks tliere is no dou1)t that 



