36 THE FROG CH. in 



3. The shoulder -girdle or pectoral arch, an inverted arch 

 of bone and cartilage nearly encircling the anterior part of 

 the trunk and giving attachment to 



4. The bones of the fore-limbs. 



5. The hip-girdle or pelvic arch, an apparatus shaped 

 somewhat like a bird's "merrythought"": it is attached in 

 front to the ninth vertebra and behind gives attachment to 



6. The bones of the hind-limbs. 



The Vertebral Column. The essential structure of a 

 vertebra may be best studied by examining any of the nine 

 from the second to the seventh : the first, eighth, and ninth 

 present certain peculiarities, and so may be left till last. 



The whole vertebra (Fig 8, B) has something the form of 

 a signet-ring with its sides produced into two outstanding 

 projections. The part comparable to the stone of the 

 ring is ventral in position, and is called the body or centrum 

 (en), the form of which is proccelous, i.e., its anterior face is 

 concave, its posterior face convex, and both faces are 

 covered with a thin layer of cartilage. The part corre- 

 sponding with the circle of the ring is the neural arch 

 (pd, /;//) : it arches over the spinal cord and is produced 

 in the middle line above into a blunt projection, the neura\ 

 spine (n. sp). From the arch is given off, on either side, the 

 large outstanding projection already referred to, the 

 transverse process (tr. pr\ which is tipped with cartilage in 

 the second, third, and fourth vertebrae. 



The neural arch gives off from its anterior face, just above 

 the origin of the transverse processes, a pair o'f small shelf- 

 like projections, the articular processes or zygapophyses (a. zyg). 

 Each has its upper surface flat and smooth, and covered with 

 a thin layer- of cartilage. A similar pair of processes spring 1 

 from the posterior face of the arch, but have the smooth, 

 cartilage-covered surface or facet looking downwards. 



