ORGANS OF REPRODUCTION 



383 



and this, with her reduced size, makes the male let go ; by this 

 croaking he is also warned off if he tries to mount a female who 

 has laid her eggs, or another male. The males remain at the breed- 

 ing pond for some weeks, and while some enter into amplexus 

 with several females, others get none. 



SPINAL CORD 



The spinal cord (Fig. 298) is an elongated, subcylindrical 

 structure, lying in the vertebral canal. It is somewhat flattened 

 from above downwards, tapers to a fine thread, the filum ter- 



d.f. 



d.h.. 



n.c. 



w.m. 



g.fn. 



p.m. 



Fig. 299. — A transverse section of the spinal cord of a frog 



c.c, Central canal ; d.f., dorsal fissure ; d.h., dorsal horn ; g.m., grey matter ; n.c, large nerve cell ; p.m., 

 pia mater ; v., vein ; v.f., ventral fissure ; v.h., ventral horn ; w.m., white matter. The dorsal and ventral 

 horns are better seen in the cord of man (Fig. 415). 



minale, in the urostyle, and swells somewhat in the regions of 

 the limbs. A transverse section (Fig. 299) shows that it is composed 

 of nervous tissue of two kinds, a grey matter inside and a white 

 matter outside (p. 533), enclosed in a connective tissue sheath, 

 the pia mater, which along the dorsal and ventral middle lines 

 passes in to some depth as the dorsal and ventral fissures. In 

 the section the grey matter extends as dorsal and ventral horns 

 on each side. In the grey matter is a longitudinal central canal, 

 which ends blindly behind, but in front is continuous with 

 cavities in the brain. 



