I.] THE FROG. 57 



j3. The 2nd, 4th, 5th, 6th and 7th vertebrae : 

 closely resembling the third, the chief differ- 

 ences being found in the varying size and 

 direction of the transverse processes, all of 

 which are smaller than those of the third 

 vertebra. 



y. The 8th vertebra : concave at each end of its 

 centrum (amphictxlous). 



8. The gth vertebra (sacrum) : its centrum ; convex 

 in front and with two convex tubercles behind : 

 its powerful transverse processes directed up- 

 wards and backwards and expanded for ar- 

 ticulation of the hip-girdle. 



The characters of y. and 8. are liable to varia- 

 tion. 



Occasionally the vertebrae may be 8 or 10 in 

 number. 



c. Examine any two vertebrae from the side, in their 

 natural positions. 



a. The zygapophy se s ; cf. supra ; note their modes 

 of articulation. 



ft. The neural spines ; short and backwardly di- 

 rected. 



y. The transverse processes ; sloping upwards and 

 backwards. 



& The inter-vertebral foramina (for exit of spinal 

 nerves); interspaces left between each pair of 

 neural arches, immediately below the zyga- 

 pophyses. 



Note that there is no corresponding passage 

 between the skull and first vertebra. 



