XIII.] THE FROG. 185 



The tenth spinal nerve leaves the neural canal by the 

 coccygeal foramen, and is distributed to the adjacent parts. 



Sympathetic. 



The sympathetic system consists of ten ganglia, connected 

 by longitudinal commissures, and situated on each side of 

 the ventral face of the vertebral column ; in the region of 

 the dorsal aorta they come into close relation with it. Each 

 sympathetic ganglion is joined by a communicating fila- 

 ment with one of the spinal nerves, and the most anterior 

 ganglia are united, in the same way, with the ganglion of the 

 ninth and tenth cerebral nerves. From this a delicate cord, 

 which must be regarded as the most anterior part of the 

 sympathetic, passes into the cranial cavity, 011 the inner 

 side of the periotic capsule, and unites with the Gasserian 

 ganglion. 



The branches of the sympathetic accompany the vessels, 

 and large branches are given to the viscera of the 

 abdomen. 



The Olfactory organs are two wide sacs which occupy all 

 the space between the mesethmoid cartilage, the antorbital 

 processes, and the premaxillse and maxilla, and open in front 

 and dorsally by the external nares, behind and ventrally 

 Iby the posterior nares. The inner faces of these sacs are 

 lined by a very peculiar epithelium, and the olfactory nerves, 

 with some branches of the trigeminal, are distributed to 

 them. 



The Eyeball is lodged in the orbit and protected by the 

 eyelids described above. It has four recti muscles which 

 proceed from the inner wall of the orbit, and are attached 

 to the circumference of the globe ; within these is a retractor 



