SUMMAEY. 241 



side ; in the turtle there is a strong prolongation, but in some species it adheres so 

 closely as to appear like a part of the par vagum. In man, branches from the cervical 

 ganglia and prolongation communicate with the cervical nerves ; but another commu- 

 nication is formed by branches sent up with the vertebral artery ; in mammalia and 

 birds, this is the chief mode of connexion with the cervical nerves ; in the turtle, 

 branches are sent upwards, but not in a distinct spinal canal; in the snake, the 

 superior cervical ganglion sends a branch to the par vagum, which may be compared 

 with the prolongation, but it cannot be separated again ; the principal way of com- 

 munication is by a branch sent downwards in an imperfect canal close to the spine ; 

 in fishes it does not exist. The first thoracic ganglion exists in the four superior 

 classes ; it is generally very large in mammalia, it is small in birds, in the turtle it is 

 membranous, but in the frog and snake there is not a distinct ganglion ; in fishes it is 

 large, and appears as the most superior ganglion. From the cervical and first thoracic 

 ganglia in man and some species of mammalia, and in others also from succeeding 

 thoracic ganglia, as well as from the par vagum, the cardiac nerves are given off; in 

 birds these proceed from the first thoracic ganglia and the par vagum ; in amphibia 

 they proceed most from the par vagum; in fishes they are not ascertained. In 

 mammalia the prolongation is continued down the thorax, either flat, like tape, with 

 small ganglia imbedded in it, or in a narrower and thicker form with more distinct 

 ganglia, for communicating with the spinal nerves ; in birds the thoracic prolongation 

 is double to some distance ; in the turtle it is also double, but the ganglia are very 

 small and connected with the spinal ganglia as in birds ; in the snake it is a fine 

 thread communicating with each spinal nerve, but not forming ganglia ; in the frog 

 there are not any ganglia, but at the connexion with each spinal nerve there is a 

 cluster of pearly vesicles containing cretaceous matter; in fishes there are small 

 ganglia at the point of connexion with the spinal nerves. In man, from the thoracic 

 portion the splanchnic nerve is given off ; in mammalia it is in some instances similar 

 to that in man, but generally it remains connected with the prolongation throughout 

 the thorax ; a smaller splanchnic nerve is also given off, but it is not more worthy 

 of distinction than many other branches ; in birds there are two principal splanchnic 



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