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Show INTRODUCTION • m . h external organs I.S cont·m ue dby The action received by t e f the nervous system, which, the nerves to the central ma~ses of the brain and spinal marin the higher animals, cons~stsn~ture of the animal, the more row. The ~ore elev.ate:n~ ~he more is the sensitive power voluminous IS the bram h 'mal the more the me-h • the lower t e am ' concentrated t ere' d. the most imperfect genera, dullary masses are dispersed, an m to melt into the general the entire nervous substance seems matter of the body. . h t . s the brain and princi- That p.art of the body whiC con adm · lied the hea · pal organs of sense, IS ca . l sensation and this has oc- When the animal has receivec a lso that this volition is cas1. 0ne d voli'tion.' it is by the nerves, a ' transmitted to the muscles. f fl. h :fibres whose contractions The muscles are bundles 0 hes y . 1 body The exten-P h ments of t e amma · · roduce all t e move . well as every :flexion 1. b d every elongatiOn, as sion of the Im s an h ffects of muscular contrac-and abbreviation of parts, are t. e ~I e arranged, both as re- I of every amma ar . tion. The bm use eds di.r ecti.O n accor d'm g to the movements It spects num er and h these motions require force, the has to mak.e ; an ;" enhard arts, articulated one over anmuscles are Inserted mto P 1 8 These parts . dered as so many ever . . other, a"'l.d may be consi b t d animals where they are m-are called bones in the v;rte ~~:ous mass: penetrated by par· ternaJ, and are formed ~ age In the Mollusca, the Crustacea, ticles of phosphate of hme. I and composed of a cal-h they are externa , . d aanrde oIunss eocrt s,h owr neyr esu bstance t h at exu des between the skm an c II d shells crusts and scales. epidermis, they areca e h .{ t the hard parts by means The fleshy :fibres are .attac e o which seem to be a conof other fibres of a gelatmous ~at~re, hat are called tendons. tinuation of the former, constit~ti~gfw surfaces of the hard The configuration of the articu a mg . d by cords or . · h' hare also restrame parts limits their motiOn,hw ~~d f the articulations, called envelopes, attached to t e SI es o ligaI me. ntfs . the various arrangements of t h"Is bony and mbu s· culat r 1asp praorma tus, and the form and proportw. n of the mem ers INTRODUCTION. 21 therefrom resulting, that animals are capable of executing the innumerable movements that enter into walking and leaping, flight and natation. The muscular fibres, appropriated to digestion and the circulation, are independent of the will; they receive nerves, however, but the chief of them are subdivided and arranged in a manner which seems to have for its object their independence of the ME. It is only in paroxysms of the passions and other powerful affections of the soul, which break down these barriers, that the empire of the ME is perceptible, and even then it is almost always to disorder these vegetative functions. It is, also, in a state of sickness only that these functions are accompanied with sensations: digestion is usually performed unconsciously. The aliment divided by the jaws and teeth, or sucked up when liquids constitute the food, is swallowed by the muscular movements of the hinder parts of the mouth and throat, and deposited in the first portions of the alimentary canal that is usua11y expanded into one or more stomachs; there it is penetrated with juices fitted to dissolve it. Passing thence through the rest of the canal, it receives other juices destined to complete its preparation. The parietes of the canal are pierced with pores which extract from this alimentary mass its nutritious portion; the useless residuum is rejected as excrement. The canal in which this first act of nntrition is performed, is a continuation of the skin, and is composed of similar lay- · ers; even the fibres that encircle it are analogous to those which adhere to the internal surface of the skin, called the 11eshy pannicle. Throughout the whole interior of this canal there is a transudation which has some connexion with the cutaneous perspiration, and which becomes more abundant when the latter is suppressed; the absorption of the skin is even very analogous to that of the intestines. It is in the lowest -.:'(]lrnf,.,. of animals that the excrements are rejected by the lllJO,enmg. their intestines resembling. a sac, with but the one Even among those where the intestinal canal has two ori- |