424 Animal Biology 



rounded prominences, the occipital condyles. The pair of prootid bones, 

 one on either side of the posterior part of the cranium (Fig. 210), forms 

 the rounded auditory capsule that encloses the inner ear. Forming the 

 dorsal roof of the cranial cavity are two bones, the frontoparietals, each 

 formed by the fusion of a frontal and a parietal bone in the young frog. 

 At the anterior end of the brain case is the tubular sphenethmoid which 

 is divided by a transverse septum into two chambers. The anterior 

 chamber is divided longitudinally by a median septum and con- 

 tains the posterior part of the olfactory sacs (nasal capsules). The 

 posterior chamber is part of the cranial cavity and contains the 

 olfactory lobes of the brain. A pair of triangular nasal hones help to 

 form the dorsal wall of the olfactory sacs. A pair of vomer hones helps 

 to form the ventral wall of the olfactory sacs and also helps to form the 

 roof of the mouth. The vomer bones bear vomerine teeth on the ventral 

 surface. The upper jaw (maxilla) consists of a pair of premaxillae, a 

 pair of maxillae, and a pair of quadratojugal hones (Fig. 210). The first 

 two bear teeth. The lower jaw (mandihle) is the only part of the two 

 jaws that moves. The jaws are attached to the cranium by a suspensory 

 apparatus, of which the squamosal (Fig. 210) is a part. The hyoid ap- 

 paratus consists of a large flat, diamond-shaped plate of cartilage in the 

 floor of the mouth cavity. Rods of cartilage and bone extend anteriorly 

 and posteriorly from its central plate. The posterior rods extend back- 

 ward to the glottis which they help to support. 



The vertebral column consists of nine vertehrae (Fig. 210) and a blade- 

 like posterior urostyle. A typical vertebra consists of (1) an oval, basal 

 centrum (for articulation), (2) neural arch through which the spinal 

 cord passes, (3) a single dorsal spine (neural spine) attached to the 

 neural arch and (4) a pair of transverse processes (except on the atlas) 

 which extend laterally for the attachment of muscles. The articulating 

 processes at each end of the neural arch are called zygapophyses. Liga- 

 ments hold the vertebrae together but allow a certain amount of move- 

 ment. 



The pectoral girdle to which the forelimbs are attached is not attached 

 to the vertebral column by bones but by means of muscles. Compare 

 this attachment with that in man (Fig. 229). The sternum ("breast 

 hone) is located on the ventral median line and is composed of a number 

 of bones and cartilages. The ventral part of the pectoral girdle consists 

 of an anterior clavicle and a posterior coracoid. Other smaller bones go 

 to make up this part of the girdle. The dorsal part of the girdle is com- 

 posed of the bony scapula dorsal to which is the cartilaginous supra- 



