70 



AGE. 



to open, that the nasal bones lengthen, that the 

 cells of the malar and upper maxillary bones 

 are enlarged, that in consequence of this ex- 

 pansion of their cavities the outer lamina pro- 

 jects, and that the lower jaw is elongated. 

 The stationary condition of the tabula vitrea 

 is conformable to the arrest in the increment of 

 the brain ; the extension of the outer table to 

 the increasing power and action of the muscles 

 attached to it ; the development of the sinuses 

 and cells to that of the voice and certain of the 

 senses ; and the projection of the jaws to the 

 increased number of the teeth. But although 

 these changes commence as early as the seventh 

 year, they are not complete till the twenty-first, 

 or even later. At this time the countenance 

 becomes settled, not merely by the full deve- 

 lopment of the muscles, which express the 

 predominant emotions of the individual, but 

 also by the complete adjustment of the bony 

 arrangements just enumerated. 



Those portions of the osseous system which 

 are employed in protecting the organs enclosed 

 by them from external compression or injury, 

 have attained a degree of growth far surpass- 

 ing that of the bones devoted to locomotion 

 and to the mechanism of sensation. The ribs, for 

 instance, defending the lungs and the heart, 

 and playing so important a part in respiration, 

 are farther advanced in the ossific process than 

 the bones of the extremities. But the most 

 striking fact of this kind is presented in the 

 spinal column. The annular portions of the 

 vertebrae which form the canal of the medulla 

 spinalis, are found strongly ossified at birth, 

 but the bodies of these bones, which are to be 

 used hereafter in supporting the weight of the 

 head and trunk, are very slightly expanded, 

 and all but devoid of earthy particles, while 

 the processes to which the muscles employed 

 in the flexion and extension of the column after- 

 wards contract attachments, are either only 

 shaped in cartilage, or may be said to have no 

 existence. 



Passing from the bones to the muscles, we 

 observe the latter no less incomplete in infancy 

 as it regards their physical characters ; they are 

 pale, flabby, and easily torn ; they contain less 

 fibrine than in after years; their contractility is 

 weak though easily excited ; and the fasciculi 

 and fibres are but loosely connected from the 

 want of the fasciae and aponeuroses which brace 

 them in later periods. As life advances, the 

 fibres become redder, more distinct, and 

 stronger. A readiness to contract is manifested 

 very early, but it is not till maturity that these 

 organs are able to maintain contraction for any 

 length of time. They suffice well for the quick 

 and buoyant motions of the lively child, but 

 fail in those violent and prolonged exertions 

 required by the labours of manhood. The 

 form of the muscles changes materially in the 

 progress of years ; thus, they swell out in the 

 middle, and occasion a great difference in the 

 proportions of the limbs. Those portions of the 

 locomotive apparatus attached to the muscles 

 and articulations, viz. the tendons and liga- 

 ments, undergo corresponding changes. In 

 infancy they are soft and gelatinous ; gradually 



they become firmer, their gelatine acquires 

 a more glutinous character, and the membrane 

 which envelopes them is more condensed. Every 

 one knows the different products obtained by 

 boiling the tendinous parts of young and adult 

 animals ; in the one they have the qualities of 

 jelly, in the other of glue. The readiness with 

 which the joints of a child are strained or dis- 

 located is likewise well known. The imma- 

 ture condition of the infant is strongly marked 

 in the ankles, which are turned inwards, and 

 would never suggest the use to which the feet 

 are to be applied, but for our familiarity with 

 the change that afterwards occurs. The car- 

 tilages and fibro-cartilages are subjected to 

 a development corresponding to that of the 

 fibrous tissue. 



Into the composition of the vocal appa- 

 ratus we know that muscular, fibrous, and 

 cartilaginous tissues enter; and, as these 

 are altered by age, the mechanism which 

 they constitute might ct priori be expected 

 to suffer similar modifications. The larynx 

 of the infant is small and almost circular; 

 consequently the lips of the glottis and 

 the superior ligaments are very short. This 

 configuration, viewed in connection with the 

 immaturity of the muscular tissue, accounts for 

 the shrill wailing cry, which is the only vocal 

 sound produced at this early period of human 

 existence, and the only one required, since 

 the quick instinct of maternal affection can 

 interpret these simple notes into an eloquent 

 language. No very appreciable alteration takes 

 place in these parts at the time when speech is 

 acquired, for this attainment has more con- 

 nection with the development and command of 

 the muscles of the pharynx and mouth, as well 

 as with the organ of intelligence, which enables 

 the human being to discriminate sounds and to 

 imitate them. Fortunately the oral and pha- 

 ryngeal muscles are some of the foremost in 

 development, being required in suction and 

 deglutition. A progressive change goes on in 

 the larynx, though it is not very evident till the 

 period of puberty in the male, when the thyroid 

 cartilage is elongated, and with it the thyro- 

 arytenoid muscle. At this epoch occurs the 

 moulting of the voice, or an accession of gravity 

 in the tones, occasioned by the elongation of 

 the parts just mentioned. The projection of 

 the pomum Adami takes place at the same 

 time. In the female larynx scarcely any change 

 occurs, and the voice in consequence remains 

 acute. We have already spoken of the facial 

 bones and their cavities, parts which exercise 

 a very decided influence on the sonorousness 

 of the voice. 



We must now hasten to the consideration 

 of the parts employed in that other distin- 

 guishing function of animals, viz., sensation. 

 There are two grand divisions of the organs of 

 sensation, those which we understand, and those 

 which we do not. The former consist of the 

 various kinds of animal mechanism whereby 

 the external causes of sensation are modified, the 

 latter of the nervous substance intermediate to the 

 external excitant, and that state of consciousness 

 which we denominate sensation. We know 



