1000 OF GENERATION. 



begins to gain upon the left ; the gall-bladder begins to appear at this time. 

 The subsequent changes chiefly consist in the consolidation of the viscus, and 

 the diminution of its proportional size. Up to the period of birth, however, the 

 bulk of the liver, relatively to that of the entire body, is much greater than in 

 the adult ; the proportion being as 1 to 18 or 20 in the new-born child, whilst 

 it is about 1 to 36 in the adult; and the difference between the right and left 

 sides is still inconsiderable. During the first year of extra-uterine life, how- 

 ever, a great change takes place ; the right lobe increases a little or remains 

 stationary, whilst the left lobe undergoes an absolute diminution, being reduced 

 nearly one-half; and as, during the same period, the bulk of the rest of the 

 body has been rapidly increasing, the proportion is much more reduced during 

 that period than in any subsequent one of the same length. According to 

 Meckel, the liver of the newly-born infant weighs one-fourth heavier than that 

 of a child of eight or ten months old ; and as the weight of the whole body is 

 more than double during the same time, it is obvious that the change in the 

 proportion of the two must be principally effected at this epoch. The liver 

 seems to be actively engaged, during foetal life, in the depuration of the blood 

 (as appears from the accumulation of meconium, which is chiefly altered bile, 

 in the intestinal canal at birth), whilst at the same time it is serving as a blood- 

 making organ ( 150, note). The general history which has just been given of 

 the development of the Liver seems equally applicable to the other glands that 

 are evolved from the parietes of the Alimentary canal, such as the Salivary 

 glands and Pancreas ; since they all seem to commence in little masses of cells, 

 formed by an increased development, at certain spots, of the layer of blastema 

 which originally constitutes its wall ; and whilst some of these cells give origin 

 to the proper tissues of each gland, others form its ducts and tubuli by their 

 deliquescence. 



1006. The Lungs also are developed in immediate relation with the upper 

 part of the Alimentary canal, their first rudiments shooting forth as a pair of 

 budlike processes (Fig. 271, a) from its cesophageal portion. These were 

 originally described by Von Bar as hollow, and as in reality diverticula from 

 the tube itself. But most later observers agree in stating that the budlike pro- 

 cesses are not at first hollow, but are solid aggregations of cells, formed by a 

 multiplication of the cells constituting the external wall of the alimentary tube, 

 into which its internal tunic is not prolonged. These gradually increase in size, 

 extending downwards by the multiplication of their component cells in that direc- 

 tion : and cavities are formed in them (probably, as in the preceding instances, 

 by the deliquescence or fusion of some of the cells of their interior), which at 

 first communicate with the pharynx by separate apertures ; these, however, 

 coalescing into one, as the channels are elongated into tubes, and the pulmonary 

 organs are removed to a distance from their point of exit. This process com- 

 mences, in the Chick, about the 4th day 



Fig- 271. of incubation ; and on the 5th or 6th, 



the lungs are completely detached from 

 the oesophagus, and each has its own 

 bronchial tube connecting it with the 

 trachea common to both (Fig. 271, &). 

 The upper portion of the lung has much 

 thicker walls than the lower ; and these 

 appear to contain a large quantity of 

 First appearance of the Lungs : a, in a Fowl at vesicular parenchyma, in which the rami- 



f our days ; b, in a Fowl at six days; c, termination fications of the bronchial tubes subse- 



of bronchus in a very young Pig. quently extend themselves. About the 



tenth or eleventh day of incubation, 

 these ramifications possess nearly their permanent character and situation. The 



