THE FROG 53 



verse process; why? In the complete skeleton, observe the 

 large gap on the dorsal surface between the skull and the 

 neural arch of the atlas. In life this gap is closed by a 

 strong membrane, but it affords a convenient place for be- 

 ginning dissection to expose the central nervous system, 

 and for dividing and destroying the central nervous system 

 in the operation known as "pithing." 



The second, third and fourth vertebrae have unusually 

 strong transverse processes; why? The ninth vertebra (sa- 

 crum) has especially strong backwardly-directed transverse 

 processes; what for? 



(c) The coccyx or so-called urostyle is a long cylinder 

 of bone with a dorsal keel; it articulates in front, by two 

 surfaces, with the body of the sacral vertebra. The neural 

 canal is continued into the anterior portion of the coccyx. 

 On the sides of the coccyx, and about the length of a ver- 

 tebra from its anterior end, are a pair of small holes through 

 which the tenth pair of spinal nerves pass out; these holes 

 correspond to intervertebral foramina. The entire coccyx 

 represents a row of fused vertebrae (compare the spinal 

 column of a tailed amphibian). 



2. The skull consists of (a) an axial portion, the cra- 

 nium, which encloses the brain ; associated with this are two 

 pairs of capsules enclosing sense organs, viz., the olfactory 

 capsules forming an anterior prolongation of the cranium, 

 and the auditory capsules forming lateral expansions of 

 the posterior region of the cranium; (b) the jaws and the 

 framework by which they are attached to the cranium, and 

 (c) the hyoid apparatus, situated mainly in the floor of the 

 mouth. 



(a) The cranium, (i) Cartilage bones of the cra- 

 nium. 



