CHAPTER 26 



STRUCTURE OF THE FULLY DEVELOPED HUMAN 



PINEAL ORGAN 



As previously mentioned, the structure of the pineal body varies 

 considerably at different ages and in different individuals, and like some 

 other embryonic and infantile organs which develop up to a certain 

 degree of perfection and then degenerate, e.g. the pronephros, the greater 

 part of the mesonephros, and the thymus gland, the pineal body normally 

 attains its maximum of development before the individual has reached 

 maturity. This maximum, according to the general estimate, occurs 

 somewhere between the ages of 5 and 7 years. Signs of degeneration are, 

 however, frequently evident before this period, and the uniform alveolar 

 appearance which is present in early infancy usually becomes less pro- 

 nounced at the end of the second year, and signs of degeneration and 

 replacement of parenchymal cells by fibroglial tissue are often seen in 

 quite young children. The parenchymal tissue becomes surrounded by 

 ingrowths of fibrovascular septa which are continuous externally with 

 the capsule. These break up the parenchymal tissue into rounded lobes, 

 as seen in Fig. 264, the pineal body of a child aged 5. This specimen 

 may, however, be regarded as exceptional with regard to the age at which 

 degenerative changes, accompanied by ingrowth of thick fibrovascular 

 septa from the capsule, have taken place, and there are instances in which 

 the uniform structure of the pineal organ present in the infant is retained 

 even in advanced age. Speaking generally, however, it is commonly 

 admitted that, although exceptions occur, there is an increase in the 

 proportion that the fibroglial constituents have to the parenchyma from 

 childhood onwards to old age. We shall, therefore, describe first the 

 structure of the pineal organ as it appears in children between 3 and 

 6 years of age, in preference to commencing the description of the organ 

 of adult individuals, in which both the parenchyma cells and the supporting 

 tissue usually show signs of degeneration. 



Besides variations in structure due to age changes there are differences 

 in appearance which are brought out by different methods of preparation, 

 and we propose, before dealing with the selective actions produced by the 

 use of special methods of modern technique, to give a short description 

 of the microscopic appearance of a section of the pineal gland of a child 



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