S6 



ELEMENTS OF MAMMALIAN ANATOMY 



ar 



Fig. 23.- 



the absence of a spinous process, and its rudimentary body. 



Its true body in the embryo becomes united to the axis as the 



odontoid process. The cranial margin 

 of the vertebral arch is prolonged at 

 each side into a process or articulation 

 with the occipital condyles (Fig. 18) 

 of the skull. The root of this articular 

 n^:-] process is pierced by a foramen giving 

 \?^ passage to the first spinal nerve and 

 the vertebral artery and vein (Fig. 24, 

 fr). From the lateral opening of this 



-Plan of a Ver- . . ^ . . i.* 1 



TEBRA. foramen {fr) a groove is continued 



s/). Spinous process; ar, ygntrad to the middle of the transverse 



articular process; MS, trans- . , , . , 



verse process; nc, vertebral prOCCSS, whcrC it Icads intO the traUS- 



LT' "'tntrut'orboX: '^erse foramen common to the first cer- 



vical vertebrae. The vertebral artery 

 and vein course through this canal (Fig. 24). 



The epistropheus (axis), or second vertebra, is characterized 

 by its dens or odontoid process, which 

 projects within the atlas, and also by 

 its elongated spinous process which 

 projects both craniad and caudad. 

 The transverse process projects 

 caudad from the body, which is flat- 

 tened dorsoventrally. This process 

 is pierced at its base by the transverse 

 foramen. 



The remaining five cervicals are 

 very similar to one another. The 

 seventh has no transverse foramen. 

 The spinous processes grow suc- 

 cessively longer from the third to 

 The transverse processes of the fourth and fifth are bifurcated, 

 the dorsal branch being called the transverse element and the 

 ventral one the costal element, since it is really the rudiment 



Fig. 24. — DoRsocAUDAL As- 

 pect OF Atlas. 

 Ir, Transverse process; nc, 

 neural canal; sp, spinous 

 process; fr, aperture of the 

 transverse foramen which 

 enters the atlas at vf; azg, 

 anterior articular process; zg, 

 posterior articular process. 



the seventh (Fig. 22). 



