38 2 DAVISON. [Vol. XI. 



The Vertebrae. 



Three divisions of the vertebrae may be recognized : cervical, 

 trunk, and caudal. There is only one bone in the first division 

 known as the axis, the atlas being anchylosed with the skull. 

 The anterior face of the axis presents two concavities for ar- 

 ticulation with the occipital condyles. There are also two 

 slight projections between the concavities, which may be called 

 prezygapophyses, as they are applied to the internal facets of 

 the condyles. On the posterior aspect are seen the postzyga- 

 pophyses descending from the backward extension of the neural 

 arch. The neural spine is only slightly developed, and there 

 are no transverse processes. This vertebra as well as all the 

 others is amphicoelous. The trunk vertebrae number sixty-two. 

 All have prominent transverse processes and high neural spines. 

 The transverse processes of the first seven or eight vertebrae 

 are laterally sulcated in their distal regions, and have short 

 ribs attached. The neural spines bifurcate posteriorly and 

 send their prongs outward on the postzygapophyses. The 

 course of each prong is V-shaped, with the apex directed 

 anteriorly. From this apex a small diapophysial spine extends 

 forward to near the anterior base of the neural spine. This 

 yorocess serves a special purpose in Amphiuma, as I shall show 

 later. The faces of the zygapophyses are in a symmetrical 

 plane, extending in an axial direction. All the trunk vertebrae 

 except the first two have small hypapophyses attached to the 

 anterior part of the body, which project anteriorly. The mid- 

 dle two-thirds of the body of each vertebra is so constricted 

 laterally as to form a rather sharp spine viscerally. 



There are two sacral vertebrae. Their processes are the 

 same as the trunk vertebrae. The caudal vertebrae number 

 thirty-seven, making a total of one hundred and one bones in 

 the spinal column. All the caudal elements except the first 

 two have prominent chevron bones. The neural spine, which 

 is so high in the trunk region, is very much depressed, and the 

 posterior bifurcations of this spine are more extensive. The 

 transverse processes are declivous and decrease in length pos- 

 teriorly as far as the mid-tail region, where they entirely dis- 



