THE PINEAL BODY 351 



pathological histology of the pineal gland, together with a 

 description and critical survey of the available clinical and patho- 

 logico-anatomical material concerning the affections of that organ. 



Anatomy. The pineal gland of man is, in the adult, a small 

 flattened body, nearly trilateral in shape, which is suspended free 

 between the anterior pair of corpora quadrigemina, with its base 

 directed forwards over the roof of the third ventricle; it is con- 

 nected with the posterior commissure of the third ventricle by 

 means of a medullary lamina issuing from its ventral portion. A 

 second medullary lamina, called the commissura habenularum, 

 issues from the dorsal part of the pineal body ; it tails off into a 

 thin band, the pineal peduncle or habenula, and this is attached to 

 a thickening, the trigonum habenulse, situated at the posterior end 

 of the optic thalami. Between the two laminse is the narrow 

 passage, blind at its caudal end, of the recessus pinealis. The 

 tela choroidea lies against the posterior portion of the dorsal 

 surface of the pineal gland ; with the anterior portion it forms a 

 pouch, the recessus suprapinealis, which opens into the third 

 ventricle. 



Embryology. From the roof of the thalamencephalon 

 (diencephalon) of the lower vertebrates, according to Edinger, two 

 buds are developed, which, proceeding dorsally, represent : (i) 

 the paraphysis; and (2) the pineal tubercle or dorsal pouch. The 

 paraphysis is not present in mammals, but the dorsal pouch is 

 represented by the recessus suprapinealis. At the boundary of 

 the thalamencephalon and the mesencephalon, are two other buds : 

 (3) the parietal vesicle ; and (4) the epiphysis. From the parietal 

 vesicle, in the lower vertebrates (fish, reptiles), the parietal organ 

 is formed (though many authors believe it to be formed from a 

 vesicular portion of the epiphysis), which breaks through the 

 cranial capsule at the parietal foramen and persists as the so- 

 called " frontal patch " ; or, in saurians, as the parietal eye, which 

 has a formation similar to that of the eye of invertebrates. The 

 changes which take place in the position of the organ during the 

 embryonal stage are shown by the course of the parietal nerve, by 

 which communication with the ganglion habenulse is effected. 

 In the loose connective tissue between the recessus suprapinealis 

 and the pineal gland of new-born infants, Marburg found a 

 structure resembling the parietal nerve and ganglion of reptiles. 

 The pineal body is developed from the epiphysal protuberance, 

 which throws out lateral buds, becomes vascular, and gradually 

 changes into a glandular structure composed of solid cell masses. 

 This gland is not furnished with ducts; it communicates with 

 the brain by means of the pineal peduncle and the posterior 

 commissure. 



Histology. In new-born infants the pineal gland consists of 

 irregular lobes held together by a small quantity of connective 

 tissue ; the lobes are composed of cells of almost the same type, 



