CHAPTER XVI 



THE FUNCTION OF THE PINEAL BODY 



MUCH attention has been devoted to the pineal body from the 

 standpoint of comparative anatomy. Its relationship to the 

 pineal eye of lower vertebrates seems to have led to the con- 

 clusion, which may, after all, turn out to be premature, that 

 the pineal body of mammals is a purely vestigial organ, and no 

 longer of any functional importance. Notwithstanding the 

 numerous investigations which have been carried out upon 

 the comparative anatomy and development of the organ, 

 there appear to be few careful and detailed descriptions of the 

 microscopical structure in Mammalia. Moreover, the number 

 of -essays in the direction of a physiological study of the struc- 

 ture are not very numerous. The general appearance of the 

 body on microscopical examination certainly suggests the 

 possibility of a secretory function, and, as we shall see, there is 

 some evidence that the pineal body controls in some way or 

 other (possibly by means of an internal secretion) the early 

 growth of the individual. 



Anatomy and Development of the Pineal Body 



The pineal body, or pineal gland (conarium), 1 is a small 

 pinkish structure situated underneath the posterior region of 

 the corpus callosum, and resting upon the anterior -elevation 

 of the corpora quadrigemina. 



A section through the diencephalon of an early human 

 embryo shows the " roof -plate " and the "floor-plate." At 

 the posterior end of the former is an elevation, which forms a 

 hollow evagination of the brain-roof the pineal process. The 

 distal extremity of this pineal process becomes enlarged to a 



1 The epiphysis of the mammal was known to the ancient Greek anatomists, 

 Galenus described it as the " Sw/ta /ca^oeftSes, KuvdpLov." Descartes, in 1649, 

 as is well known, considered it to be the seat of the soul. 



385 25 



