632 Prof. Dendy. Structure, etc., of the Pineal Oi^gans [June 22, 



together by radiating threads of cytoplasm to form a syncytium. In 

 connection with this epithelium there is a very conspicuous but irregular 

 network of nucleated cytoplasm lying in the paraphysial lumina. The 

 nuclei in this network are very poor in chromatin and undergo amitotic 

 division. Sometimes little rounded knobs, covered with the syncytial 

 epithelium, project from the wall of the paraphysis into its various cavities. 



I have already described the origin of the two pineal organs from the 

 brain-roof, and how, from its first appearance, the one which is destined to 

 give rise to the pineal eye usually lies a little to the left of the other, which 

 will give rise to the pineal sac. I am now able to confirm Sehauinsland's 

 subsequent observation that these two vesicles are at first in open communi- 

 cation with one another, but I do not consider that this need prevent us from 

 regarding them as members of an originally symmetrical pair, and fresh 

 evidence in favour of this view is put forward in the present memoir. 



The opening of the pineal sac into the third ventricle, between the 

 superior and posterior commissures, closes up at a comparatively early date, 

 but vestiges of the connection remain in the " infra-pineal recess " and in the 

 " pineal tract " by which the pineal sac of the adult remains connected with 

 the brain-roof. The pineal sac grows upwards in close contact with the 

 posterior wall of the dorsal sac, to which it is firmly attached by the 

 2na mater, and its upper end turns forwards over the roof of the dorsal sac 

 and over the upper part of the paraphysis. In the adult it is a relatively 

 large organ and takes an important part in the formation of the pineal 

 complex. It remains tubular, but its walls become greatly folded and much 

 thickened. They are supplied with blood by the anterior and posterior 

 pineal arteries and drain into the smws longitudivalU. There is little or no 

 evidence that the pineal sac is a glandular body, but, on the contrary, its 

 histological structure points to a sensory function. Its thick wall is made 

 up of nucleated radial supporting fibres, numerous ganglion-cells and nerve- 

 fibres, and numerous sense-cells whose inner ends project slightly into the 

 lumen of the organ. These constituents are identical with those which 

 occur in the retina of the ])in(!al eye, and their arrangement is essentially tlie 

 same. In one ctlhc, in which the tip of the pineal sac projected unusually far 

 forwards, so as to come under the influence of the light passing through the 

 transparent parietal plug, a pigmented evagination of the wall of the pineal 

 Hac was formed, and the reHeni])lance to the retina of the ])ineal eye became 

 still more oljvious. These ol)servations, conlinniiig and extending earlier 

 obeorvations by Hoffmann, Gisi, and myself, greatly strengthen the view 

 that tlie ])iiio!d sac and pineal eye are bilaterally homologous .structures. 



'J"he i)in(!al sac is ])r()vi(l(!(l with a wcill-dcvcloped nerve, composed of nnn- 



