36 THE FROG CHAP, ra 



3. The shoulder-girdle or pectoral arch (Figs. 8 and 12), 

 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 (Figs. 8 and 14), an 

 apparatus shaped somewhat like a bird's " merry- 

 thought " : 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 corresponding with the circle of the ring is the 

 neural arch (pd, Im) : it arches over the spinal cord and 

 is produced in the middle line above into a blunt projec- 

 tion, the neural 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 of 

 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 from the posterior 



