NERVOUS SYSTEM IN THE INVERTEBRATA. 47 



10. Panniculus carnosus best marked in the echidna, the hedge- 

 hog, the porcupine, the manis, the tatu, the marsupiata, and The 

 thin-skinned ruminants ; less so in the pachydermata, and absent 

 from some, as the hog. It is found in monkeys, but not in the 

 chimpanse. 



11. Lattismus dorsi, teres major, &c, are very powerful in the 

 mole and ant-eaters. 



12. The plantaris, which is rudimental in man, is large in mon- 

 keys and some quadrupeds. 



13. Man is characterised by the magnitude of his buttocks, thio-hs, 

 and calves. 



CHAPTER VII. 



ON THE NERVOUS SYSTEM IN THE INVERTEBRATA. 



This system, when perfectly developed, consists of an internal or 

 central, and an external or circumferential portion ; to the latter 

 belong the nerves and ganglions ; to the former, the spinal cord, the 

 medulla oblongata, the cerebellum, and the cerebrum. The nervous 

 system presides over the movements of our muscles and the sensi- 

 bility of our bodies; by it we are connected with surrounding 

 objects, and an injury inflicted on any part of the body, at once 

 declares the extent of its distribution, as well as the close relation 

 that subsists between its several parts. 



The nervous system has been detected in every division, although 

 not in every class, of the animal kingdom : it commences its develop- 

 ment at the circumference, and grows towards the centre, and its 

 forms corresponds pretty closely with that of the body of the animal. 



The nervous matter is extremely soft in the inferior grades of 

 animals, as well as in the embryo of the higher classes ; and its 

 colour presents some variety, being bright red in the helix stagnalis • 

 blackish red in the aplysias ; and bright yellow in the common fresh 

 water muscle. The nerves are composed of tubes filled with minute 

 globules. The brain is also composed of globules, eight times 

 smaller than those of the blood, larger and more numerous in the 

 medullary, than in the cineritious substance, and in the former dis- 

 posed in lines which gave it its fibrous character. 



Cyclo-neura, Grant. — In the two first classes of this division, 

 the polygastrica and the porifera, no nervous filaments have been 

 detected, yet, from their active movements, their sensibility to the 

 impression of light, and their consciousness of each others approach, 

 it is but reasonable to infer the existence of a nervous system in 

 them, though from its transparency or some other cause, it cannot 

 be demonstrated. Both nerves and ganglions are found to exist in 

 the three remaining classes of the radiata. Distinct nervous fila- 

 ments surround the muscular foot of the actinia; and in the 



