FROG: EXTERNAL FEATURES AND BODY-WALL 29 



transverse process, which is especially large in the sacral 

 vertebra. At the end of each transverse process is a 

 small knob of cartilage which represents a rib. That part 

 of the arch which lies between the transverse process of 

 each side and the neural spine is known as a lamina, and 

 the part between the centrum and the transverse process is 

 a radix or pedicle. Each vertebra is jointed to those in 

 front and behind it by projections, one on each side at 

 each end of the 



arch, at the junction n.s. lam. 



of transverse pro- 

 cess and lamina, 

 known as zygapo- 

 physes. The zygapo- 

 physes in front of 

 the vertebra (prezy- 

 gapophyses or su- 

 perior articular pro- 

 cesses') have each a 

 flat surface facing 

 upwards. Those 

 behind (poslzygapo- 

 physes or inferior 

 articular processes) 

 have flat surfaces 

 facing downwards 

 which fit on to the 

 surfaces of the prezy- 

 gapophyses and slide 

 over them as the 

 backbone bends. 

 The front and hind 

 edges of each pedicle are concave, forming thus inter- 

 vertebral notches, and the adjoining notches of two 

 vertebras form an intervertebral foramen, through which a 

 nerve passes from the spinal cord. Most of the centra 

 are hollow in front and rounded behind and thus fit to- 

 gether by ball-and-socket joints, but the first vertebra has 

 in front two hollows, which serve as sockets for two 

 knobs, known as the occipital condyles, on the hinder end 

 of the skull, while the eighth is hollow behind as well as in 



Fig. II. — Vertebra; of a frog. A, fourth 

 vertebra, seen from in front ; B, sixth 

 and seventh vertebra from the right. 



az., Prezygapophysis ; cett., centrum; i.n., inter- 

 vertebral notch ; lam., lamina of neural arch ; 

 n.a., pedicle of same; n.c. t vertebral foramen; 

 n.s., neural spine ; $ed., pedicle ; pz,, postzyga- 

 pophysis ; r.c, cartilage at end of transverse 

 process ; tr. , transverse process. 



