AGEi. 



that of inferior animals. The urine >s retained 

 a shorter time in the bladder ; it is more aqueous 

 and less impregnated with saline and animal 

 ingredients than in after life ; there is also a 

 particular deficiency of urea. Of the intes- 

 tines we have already spoken ; their contents 

 are copious but less feculent than they after- 

 wards become. The perspiration affords a si- 

 milar character to that of the other excrernenti- 

 tious secretions, being more aqueous, less sa- 

 line, and less odorous. On the whole it may 

 be said that less activity is indicated in the 

 egestlvc than in the ingest ive system. 



Of the defensive organs, or those which 

 are exposed to surrounding agents, we may 

 remark, in general terms, that although fully 

 adequate to the demands of the infant under 

 the circumstances of his existence, they acquire 

 a development proportionate to his growing in- 

 dependence of the care of others. The skin 

 increases in firmness, and the epidermis in thick- 

 ness ; the sebaceous follicles become larger and 

 more numerous, and the hair is more abundant. 



There is a portion of the nervous system 

 which we have every reason to consider more 

 related with the functions which have been just 

 reviewed, than with those of the animal life, and 

 which might a priori be expected to bear 

 a corresponding ratio of developement. We 

 allude to the ganglions; they appear to be 

 fully formed at birth, but what changes they 

 undergo between that period and maturity we 

 do not profess to know. In old age their 

 tissue is found hardened, shrunken, and of a 

 greyish colour. (Bichat.) 



The changes that we have next to take 

 notice of are of a totally different character 

 from the foregoing. They consist not merely 

 in augmentations of size, correspondent ly with 

 the general increment of the body, or in modi- 

 fications of organs according to the altered 

 circumstances under which they have to act, 

 but in processes essential to the completeness 

 of certain organs. These are the parts em- 

 ployed in locomotion, voice, sensation, and 

 thought. We shall begin with the osseous 

 system. 



Bones are not subservient to locomotion 

 only ; they have, in some parts of the body, 

 the important office of enclosing and defending 

 from external injury the more delicate organs of 

 the system. We shall find, therefore, that in 

 the young animal, according as they fulfil the 

 one office or the other, their development will 

 differ. But whatever be the functions of the 

 bones, they require, for the perfection of that 

 function, three mechanical properties, firm- 

 ness, lightness, and tenacity. They must not 

 admit of flexion, and, at the same time, the 

 density of their substance must not render 

 them cumbrous by weight, or brittle in texture. 

 To present these three conditions, the organs in 

 question consist of two principal ingredients, 

 an animal matter and an earthy matter, most 

 intimately interwoven ; the one preventing such 

 vibrations as would occasion risks of fracture, 

 the other affording the necessary strength in 

 supporting weights,and in resisting the divellent 

 tendencies of antagonist muscles. The pro- 



portion which these parts bear to each other 

 varies with the ages of the human subject. 

 Viewed as a part of the system devoted to the 

 life of relations, bones are used as pillars of 

 support, as levers in various attitudes and mo- 

 tions, and as points cTttppui to the muscles and 

 tendons. On examining the constitution of 

 these portions of the osseous system in the 

 new-born infant, we find the quantity of cal- 

 careous salts comparatively small, and even 

 the animal substance softer than in later pe- 

 riods, in consequence of the greater ratio of 

 gelatine. In growth these proportions undergo 

 a gradual alteration ; the gelatine is diminished, 

 the cartilage becomes firmer, and both give 

 way to the deposition of earthy particles : in 

 the increase of density produced by this de- 

 position consists the process of ossification. 

 To particularize the incompleteness of the 

 osseous system would require us to enter upon 

 the anatomy of almost every bone in the body, 

 an investigation incompatible with the limits of 

 this article. Some idea of it may be obtained 

 from the fact that all the epiphyses of the long 

 bones, and the greater number of the apophyses 

 are as yet but cartilaginous ; they derive their 

 ossification, not from an extension of the pro- 

 cess in the bones to which they are attached, 

 but from ossific centres within their own 

 spheres. In the tarsus the only bones in 

 which ossification has commenced are the as- 

 tragalus and os calcis. The carpus is entirely 

 cartilaginous. The os innominatum of the pel- 

 vis consists of three separate bones ; ossifica- 

 tion has but just commenced in the descending 

 ramus of the pubis, and the ascending part of 

 the ischium ; and the consolidation of the pel- 

 vis is not complete till after the thirteenth year. 

 The long bones have no central medullary 

 cavity in the early periods of intra-uterine life ; 

 but in the foetus at its full term, the animal 

 matter which occupied that space has begun to 

 be absorbed, and the deposition of osseous 

 matter takes place in the form of a cylindrical 

 sheath, so that the canal exists at this period, 

 though in an incomplete state. The medullary 

 canal is analogous to the cells of the short and 

 flat bones, and of the extremities of the long 

 bones, which are also incomplete in infancy. 

 The shape of the cylindrical bones is mani- 

 festly different from that which they afterwards 

 assume ; thus there is a much smaller dispro- 

 portion between the diameters of the extremi- 

 ties and that of the shaft ; the surface is less 

 furrowed by sinuses or roughened by ridges; 

 differences exactly corresponding to the imper- 

 fect development of the muscles, which, when 

 more bulky in their middle portions, require a 

 larger space for their accommodation about 

 the body of the bone, and when stronger in 

 contraction, require attachments that will match 

 them in firmness. The osseous system is not 

 complete till after the age of twenty. 



There is no part of the skeleton in which we 

 have a more striking illustration of its gradual 

 development than in the bones of the face aiid in 

 the cranium. It is not till the seventh year that 

 a separation begins to take place between the 

 tables of the skull, that the frontal sinus begins 



