M E G A L O N y X . 21 



passes on the outside of tlie contiguous articular process forward and inward, and 

 then becomes continuous with a foramen, piercing the base of the transverse pro- 

 cess downward and forward. The channel next continues a short distance on 

 the under side of the transverse process, and then communicates with a second 

 foramen piercing its base forward and upward. It now turns inward and forward 

 from the latter foramen, and becomes continuous with a third foramen piercing 

 the abutment of the upper arch of the bone above the position of the anterior 

 articular process and turning inward and forward to the spinal canal. 



Inches. 

 Greatest transverse diameter of the atlas ........ 6| 



Length at the conjunction of the arches ........ 3J 



The body of the axis (PI. VII, Fig. 3), with its process, is three and a half 

 inches long ; and posteriorly it presents a transversely elliptical surface, twenty-two 

 lines wide and sixteen deep. The inferior surfiice possesses a prominent median 

 ridge, upon each side of which it is concave. The odontoid process inferiorly sup- 

 ports an oblique, discoidal, articular facet for conjunction with the atlas; and 

 superiorly presents a smaller facet for contact with the transverse ligament. 



Viewed laterally, the spinous process presents a broad surface, terminated by an 

 irregularly convex margin, at its widest part measuring three inches. Posteriorly 

 the spinous process is excavated into a deep and wide vertical concavity, which 

 expands below upon the roof of the spinal canal. The abutments of the spinous 

 process or the sides of the spinal arch above the posterior articular facets, are 

 nearly two inches wide, but between these facets and those anterior, they are only 

 an inch wide. 



The spinal canal is obcordiform, and anteriorly measures about twenty lines in 

 its long diameter) but, transcends this gradually by expansion posteriorly. The 

 anterior articular facets are oval in outline and slightly convex. Those posterior 

 are elliptical and transversely convex, and are directed downward. The transverse 

 processes are elongated pyramidal, project outward and backward at an angle of 

 about 45°, and posteriorly measure two inches and a quarter in length. The foramen 

 for the vertebral bloodvessels pierces the base of the transverse process from behind 

 outward and forward, and is visible laterally just behind the anterior articular 

 process. 



The remaining three cervical vertebrse, apparently the third, fifth, and seventh, 

 have a demi-cylindroid body expanding posteriorly. (PI. VII, Fig. 4.) The anterior 

 surface of the body is transversely demi-oval and convex ; and the posterior surface 

 is oval and slightly concave. 



The spinous process is long, tapering, and trilateral ; and presents an acute 

 margin anteriorly, and a thick, vertically grooved one posteriorly. In the seventh 

 vertebra it is three inches in length, and has an irregular tuberous extremity. 

 The spinal canal is trilateral, and has its vertical diameter the deeper in the third 

 vertebra ; but in the other two the transverse diameter is the greater. The arti- 

 cular processes form four projecting angles to the base of the spinal arch. Those 

 anterior are most prominent, and present a concave facet directed upward and in- 



