8-4 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



described by Bourne ('84, p. 86), Benham ('94, p. 477), Adolpbi ('96, 

 p. 133), aud others. But such masses may, iu my opiniou, better be 

 interpreted as ankylosis, symmetrical if the line of fusion be transverse 

 to the axis of the column, or unsj^m metrical if the line of fusion has been 

 oblique. This is borne out by the fact that near, though not necessarily 

 contiguous to such an unsymmetrical mass, there is usually found a comple- 

 mentary mass (see Benham, '94, pp. 477, 478) ; i. e. if by oblique fusion 

 we have a mass containing one right half-vertebra and two left halves, 

 we shall find near by another mass representing one left half-vertebra, 

 and two right halves. The vertebrae lying between these two masses 

 will be morphologically oblique, their two halves iu each case belonging 

 to different somites, although the adjustment of growth may have 

 brought these to an apparently normal position, with transverse axis at 

 right angles to the main axis of the column. That the right and left 

 halves of a vertebra may slide upon each other, is held by Adolphi 

 ('96, p. 136) to be confirmed by embryological evidence. Such unsym- 

 metrical masses have not been accompanied by correlative asymmetry 

 in musculatui'e and nerves where the soft parts have been described. 



Symmetrical fusion of vertebrae has been described by Howes ('93, 

 p. 295), Adolphi ('95, p. 466, and '96, p. 122), and others. An actual 

 increase in number of vertebrae, and also an indicated increase by gi'oov- 

 ing and partial splitting of vertebrae, and by bifurcation of transverse 

 processes, have been noticed by Bourne ('84, p. 87), Benham ('94, p. 478), 

 and others. The cases of actual increase described were in Anura, and 

 resulted from separation of the anterior portion of the urostyle as a 

 supernumerary vertebra. Adolphi ('95 and '96) has recorded forty-three 

 cases of vei'tebral fusion in Bufo, Pelobates, and Eana, and has deter- 

 mined the nerve relations. He finds that in such cases of fusion the 

 spinal nerves are not suppressed, but emerge through foramina in the 

 fused mass ; they are, however, liable to be weaker than normal. 



Such supposed direct evidence of intercalation and excalation is capa- 

 ble of being interpreted as pathological, rather than as a disturbance 

 tending primarily to alter the serial number of metameres, — especially 

 since it is almost entirely confined to the skeleton, without involving 

 musculature or nerves beyond the narrow limits necessitated by local 

 accommodation to the distorted vertebrae. No evidence of the inherit- 

 ance of such abnormalities has yet been offered. Such would be valu- 

 able as determining whether or not these variations show persistence. 

 If so, it would indicate that they are sports ; if not, the pathological 

 interpretation would be strengthened. 



