BULLFROG AS TYPICAL VERTEBRATE ANIMAL 



85 



arches supporting the gills, and evidence of this is seen when the 

 frog tadpole breathing with gills transforms to the frog breathing 

 without gills. 



The upper jaw consists of a pair of short premaxillary bones in 

 front, a pair of long maxillae forming the sides, and a pair of short 

 quadratojugals as the posterior portions. The premaxillae and 

 maxillae each bear a row of small conical teeth. The lower jaw is 

 formed primarily of a cartilaginous rod known as Meckel's cartilage. 



At the extreme anterior tip of the jaw the rod is ossified to form 

 two small bones, the mentomeckelian bones. It is subsequently cov- 

 ered anteriorly by a dentary bone and posteriorly by an angulo- 

 splenial bone. The jaws are attached to the cranium by a combina- 

 tion of three bones on each side, the squamosal, pterygoid, and 

 palatine, to form a suspensory mechanism. 



Dorsal fissure 



GraywatieK 

 Zygapophysis _ 



White mattec 



Central canal 

 Dorsal root- 



Ventmal fissure. ^/ 



___Neural spine 



Neural arch 

 — Transverse process 



Duta mater 



_ Qanglion 

 Pia mater 



^. /verve fcrunh 

 Ventral root 



Centrum 



i:'i&. 2b.— structure of a single vertebra and cross section of the spinal cord of 

 J^^\ (Redrawn and modified from Holmes, Biology of the Frog, by permission 

 of The Macmillan Company, after Howe, Atlas of Zootomy.) 



The vertebral column is made up of a series of nine typical verte- 

 brae and a long bone, the urostyle, which includes a fusion of the 

 vertebrae from the tadpole tail with the tenth. 



In the neck region, there is one cervical vertebra, the atlas, which 

 articulates with the skull. This is followed by seven trunk vertebrae, 

 then one sacral vertebra whose processes support the pelvic girdle, 

 and finally the urostyle, which contains all of the caudal vertebrae 

 fused into one piece. 



The basal portion of the tj^pical vertebra is kno\vn as the centrum. 

 The centrum is concave in front and convex posteriorly, and there- 

 fore is procoelous. Attached to the centrum is a bony ring, the 

 neural arch, which extends dorsally from the centrum around a por- 

 tion of the spinal cord. The neural arch has extending from its sides 



