THE FROG. 95 



and immediately in front of the pyriformis 

 muscle (Sect. H. 5. c). 



(S. The anterior ly77iph-heart ; lying in an inter- 

 space between the small muscles {intertrans- 

 versi) which pass between the transverse pro- 

 cesses of the third and fourth vertebrae. Best 

 seen on slitting open the body-wall ventro- 

 laterally and cutting into the cisterna magna. 



The cartilaginous free end of the transverse 

 process of the third vertebra is expanded (of. 

 Sect. G. 3c) for protection of the above. 



The nervous system. 



I. The cerebrospinal axis and neural canal. Take a 

 recently-killed frog and divide the skin along the 

 dorsal middle line and reflect it on each side ; re- 

 move the muscles which overlie the arches of the 

 vertebrae, and open the neural canal as follows. Di- 

 vide the membrane {vertebra-occipital ligament) which 

 passes between the ist vertebra and occiput; then 

 introduce one blade of a small, but strong, pair of 

 scissors into the cranial cavity, and cut away bit by 

 bit the bones which form the roof of the skull, 

 taking care that the point of the scissors does not 

 injure the brain. Next remove, in a similar manner, 

 the tops of the vertebral arches and the head of the 

 urostyle. In all probability a chalky fluid will be 

 met with clouding the water and concealing the un- 

 derlying organs (secretion of the periganglionic glands 

 (cf. p. 32); if so, wash carefully until clean. There 

 will thus be exposed 



a. The cerebrospinal axis ; filling the greater part 

 of the neural canal ; it can be resolved into 



