242 SUMMARY. 



nerves, the upper accompanying the coeliac artery, the lower communicating with the 

 renal capsule, and accompanying the superior mesenteric artery ; the semilunar 

 ganglion is very small; in the turtle there is the same disposition, but instead of a 

 semilunar ganglion, a plexus is present ; in the snake this plexus is more extended, 

 and has still less of the form of the ganglion ; in fishes there is a considerable fleshy 

 ganglion ; whether there be a semilunar ganglion or a plexus, there is a similar distri- 

 bution to the several organs. The lumbar and sacral portions in mammalia resemble 

 those in man ; the ganglia in birds, amphibia, and fishes, are much smaller and more 

 indistinct. The spermatic nerves in mammalia are generally less complicated than in 

 man ; in birds they proceed from the lower splanchnic nerve, at its connexion with the 

 renal capsule ; in amphibia numerous branches are given off to the ovary and the 

 long oviducts ; in fishes they proceed from the sympathetic, at the lower part of the 

 abdomen. The renal nerves in mammalia are generally rather more simple than those 

 in man ; in the other classes they have a more extended origin. The termination of 

 the sympathetic in the single ganglion is continued on the caudal artery into the tail. 

 In mammalia, the hypogastric plexus is similar to that in man for supplying the 

 reproductive and urinary organs, and the lowest portion of the intestines, in the male 

 and female, after a conjunction with some of the sacral nerves ; its branches are, 

 therefore, differently disposed according to the sex ; in birds it is resembled by the 

 long nerves, formed by the spinal and sympathetic for the parts about the cloaca and 

 tail ; in amphibia it is still more simple. 



The nervous system has a modified consistency in accordance with that of the 

 body. However different the forms of animals may be, there are appropriate arrange- 

 ments of the centres for giving the required powers, and nerves adapted by size and 

 length for allowing free motions of all the parts, either in the interior of the body for 

 performing vital functions, or in the exterior for completing sensation and motion. In 

 the organ for each sense there is a resemblance of structure and shape appropriate for 

 its peculiar function. In the mode of the origin of the nerves of the special senses 

 there is a considerable similarity in the several classes of animals, but there are also 

 degrees of complexity. There is not much variation in the local origins of the 



