230 



THE FROG— THE PLATANA 



(e) The tenth or coccygeal nerve, which passes through a small aperture in 

 the side of the urostyle, and is distributed to the walls of the cloaca 

 and urinary bladder. It is connected by a small branch with the 

 sciatic nerve. 



[In the Platana the seventh, eighth, and ninth nerves run obliquely backwards. 

 The eighth and ninth unite to form the sciatic plexus, which gives. rise to a large 

 sciatic nerve eoctending along tlie thigh and down the leg. The sciatic plexus 

 also receives a branch from the seventh nerve. The seventh nerve gives rise to a 

 cruralis nerve dividing into several smaller branches and supplying the skin and 

 muscles of the outer surfaces of the thighs. The sciatic nerve gives off a smaller 

 semimembranosus nerve to the semimembranosus muscle. 



The coccygeal nerve is very variable in the Platana. It may be present on each 

 side of the spinal cord, or only on one side, or it may be absent] 



A B 



Fig. 83. — ^A. Spinal Nerves and Sympathetic Nervous System (left side only) of Sana ; 



and B. of Xenopus. 



2. The Sympathetic Nervous System. 



This system is connected with the spinal and cranial nerves. It consists of 

 a cord or chain of gangha, on each side of the body, joined together by a longi- 

 tudinal cord. Each ganglion is connected with a spinal nerve by a short branch 

 (ramus communicans). Each cord extends alongside the vertebral column and 

 the dorsal aorta. There are ten s}Tnpathetic gangha altogether. The first 



