4 THE SKELETON OF THE CAT. 



The vertebral arch (each half of which is sometimes called 

 a neurapophysis) rises on each side from the cranial two-thirds 

 of the dorsolateral angle of the centrum, as a thickened por- 

 tion, the radix or pedicle (Figs. 2 and 3, e), which forms the 

 ventral half of the lateral boundary of the vertebral canal. 

 From the dorsal end of each radix a flat plate of bone, the 

 lamina (/), extends caudomediad to join its fellow of the 

 opposite side and form the vertebral arch. Owing to the fact 

 that the radix rises from only the cranial two-thirds of the 

 centrum there is left in the caudal border of the vertebral arch 

 a notch bounded by the radix, the lamina, and the centrum. 

 There is also a slight excavation of the cranial border of the 

 radix. When the vertebrae are articulated in the natural posi- 

 tion, these notches form the intervertebral foramina (Fig. 4, 

 d), for the exit of the spinal nerves. 



At the junction of radix and lamina the arch is produced 

 craniolaterad into a short process, the transverse process {g), 

 knobbed at the end. On the ventral face of its free end the 

 transverse process bears a smooth facet, the transverse costal 

 facet or tubercular facet (Fig. 4, c), for articulation with the 

 tubercle of a rib. 



On the dorsal face of each lamina at its cranial border is a 

 smooth oval area, the cranial articular facet (superior articular 

 facet of human anatomy) (Figs. 2 and 3, h). Its long axis is 

 oblique and it looks dorsolaterad. The slight projections of 

 the cranial edge of the laminae on which the facets are situated 

 are the inconspicuous cranial articular processes (prezyga- 

 pophyses). 



On the ventral surface of each lamina at the caudal border, 

 near the middle line is a similar area, the caudal articular 

 facet (inferior articular facet of human anatomy) (/) ; these 

 occupy the ventral surfaces of two projections which form the 

 caudal (inferior) articular processes (i)ostzygai)ophyscs) {J). 

 These are separated by a median notch. When the vertebrae 

 are in their natural position the caudal articular facets lie dorsad 

 of the cranial facets and fit against them. They thus strengthen 

 the joint between contiguous vertebrae, while permitting slight 

 rotary motion. 



