218 R. W. SHUFELDT 



as a thickened haemal spine. Posteriorly, it offers the usual 

 cup-like articulation of the third cervical vertebra. 



This to some extent aborted or vestigial axis vertebra lacks 

 both pre- and postzygapophyses ; while, when the cervical verte- 

 brae are duly articulated as in life, the prezygapophyses of the 

 third vertebra extend forward, to articulate with the post- 

 zygapophyses of the atlas, which are elongated, and extend 

 backward and outward for that purpose, the circular articular 

 facets being, on their mesial aspects, somewhat in advance of the 

 end of the process on either side. 



These and other conditions are distinctly foreshadowed through 

 what occurs in the very young and subadult specimens of Amyda 

 ferox. Through the kindness of Mr. F. W. Walker, of Orlando, 

 Florida, and Mr. Edward S. Schmid, of Washington, I have been 

 abundantly supplied with such material, and, further, I am 

 greatly indebted to Dr. Charles Judson Herrick, of the University 

 of Chicago, for having had made for me, by his assistant, Miss 

 Jeannette Obenchain, nearly forty microscopic slides of the 

 cervical region of the vertebrae column in young Amyda ferox. 

 These present the morphology of the cervical vertebrae at these 

 young stages in the soft-shelled turtles. The series well demon- 

 strates the several centers of ossification of the atlas; the fact 

 that the centrum of the axis is formed in the same line and in 

 the same manner as the centra of the other cervicals of the 

 column, and clearly shows its articulation with the atlas anteriorly 

 and the third cervical which immediately follows it. 



Counting, then, the first two bones in the neck of the turtles 

 of the genus Amyda as the atlas and axis, the third cervical, or 

 the bone next in order, is narrow and much elongated — char- 

 acters that gradually change as we proceed backward through 

 the series to include the eighth from the skull (figs. 3 to 5), 

 They become progressively shorter and broader, with forms that 

 are well shown in the accompanying plates. 



It was Huxley's opinion that "In a great many Vertebrata, 

 the first and second cervical or atlas and axis vertebrae undergo 

 a singular change; the central ossification of the body of the 

 atlas not coalescing with its lateral and inferior ossifications, but 



