AXIAL BIFURCATION IN SNAKES. 



BOSWELL HILL JOHNSON. 



This paper contains descriptions and skiagraphs of thirteen 

 two-headed snakes, a recapitulation of others previously de- 

 scribed, and a concluding general treatment of this abnor- 

 mality. 



In the belief that the skeleton should be the basis of descrip- 

 tions of cases of axial bifurcation, I have studied as many of 

 these abnormalities as could be obtained from American mu- 

 seums. It seemed to me that skiagraphy, offering an opportu- 

 nity for such skeletal study, might reveal some possible laws 

 of this abnonnalitv. The numerical data for the thirteen in- 

 dividuals is given in Tables I and II. 



Case I. This is the case recorded as ^^a small double-headed 

 snake from South America,'' ^o. 856, in the descriptive Cata- 

 logue of the Anatomical Museum of the Boston Society for 

 Medical Improvement. This museum is now a part of that 

 of the Harvard Medical School. This specimen [Plate 

 XXXII, rig. 1] was found to have scales impermeable to 

 Roetgen rays, the only one of the snakes in which this was the 

 case. The snake is in so bad a condition as to render specific 

 determination difficult. It is probably Tropidonotus fasciata 

 fasciata Linn., the range of which is the Austroriparian Region, 

 or the Southern States. A normal specimen of this species, 

 however showed the scales to be permeable to the Roentgen rays. 

 The arrangement of the shields upon the dorsal aspect of the 

 head is unusually irregular as Plate XXXIII, Figure la, 

 shows. The angle of the sagittal planes of the skulls is 90°, 

 that of the frontal planes is about 145° with the angle facing 

 dorsally. Measurements upon the two divisions show that the 

 left is less than a millimeter shorter and slightly broader than 



the right division. 



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