170 PECULIARITIES OF INTERNAL STRUCTURE. 



an old man in whose brain it was deficient, is regarded by 

 Blumenbach* as a rare anomaly of structure f. 



The position of the heart in biped man differs from that 



♦ De G. II, Var, Nat. p. 44-. From the very accurate researches of the 

 "Wexzels it appears that a deficiency of the acervulus is not so uiifrequent 

 as had been represented by Soemmerring; and they found, on the other hand, 

 that the latter excellent anatomist has not been correct in fixing (he fourteenth 

 year as the date of its earliest appearance : they have met with it from the 

 age of seven. Tlicy mention six instances, in which the acervulus did not 

 exist. De penitiori Structura Cerebri //omznw e< Urw^orMW, Tubingoe, fol. 

 lSI2,p, S16. 



+ The human encephalon undergoes considerable changes after birth, in its 

 entire mass, in the proportions of its parts, and in the texture and consis- 

 tency of its substance. The gradual evolution of the mental faculties cor- 

 responds to these alterations; which, indeed, accord with the slow deve- 

 lopcment of the human frame in other respects, Tlie Wenzels have 

 afforded accurate information on some points. In an embryo of five months 

 they found a brain of 720 grains ; cerebrum of 683; cerebellum of 37, which 

 is a ratio of the former to the latter as 18|-|- to 1 : at eight months the num- 

 bers were 4960, 4610, 350, or as IS-/- to 1 : at the time of birth, as 6130, 

 5700, 450, or 12f to I : at three years, 15,240, 13,380, 1860, or 7^c_ to 1 : 

 at five years, 20,250, 17,760, 2490, or 7-^^ to I. From fifteen to eighty- 

 eight the highest numbers occurred in a youth of the former age; they were 

 24,420,21,720,2700, or 8_4_ to 1. Tab. S. 



Soeiimerring observes, in the explanation of his beautiful tabula baseos 

 encephali, p, 13, that the human brain has reached its full developement at 

 three years of age: the Wenzels afSrm that this is not the case till seven, when 

 they observe, "cerebrum hominis et quoad totum et quoad si ngulas partes 

 absolutum esse videtur." P. 247. If the perfect state of the brain be con- 

 sidered to include the proportionate developement of parts, the entire size 

 and weight, the consistence and cohesion of the mass, and the state of vascu- 

 lar supply characterizing the adult, we must fix as its era a much later pe- 

 riod than the seventh year. I apprehend that the brain of animals will be 

 found nearly perfect in its organization at the time of birth^ and, conse- 

 quently, that a comparison of man and animals, in this point of view, will 

 disclose a remarkable point of distinction between them. The medullary 

 stria? of the fourth ventricle are not seen at birth : their appearance in the 

 first year, and that of the acervulus in the seventh, are regarded by the 

 Wenzels as great peculiarities of the human brain, since that of the mam- 

 malia exhibits no such developement of new parts after biith. Cap. 27. 

 This seems to me a confined and inadequate view of a point, which, in itb full 

 extent, is of great importance. 



