50 Journal of Comparative Neurology. 



amining the brain from the superior side and paying attention to 

 the pineal organs we find the skin attached to the intermediate 

 part and connective tissue of the skull. In transverse sections of 

 this region we find numerous filaments of this connective tissue 

 uniting the corium to the skull. The superior wall of the skull 

 above the diencephalon consists of a connective tissue transparent 

 as glass, through which we get a glimpse of the brain, and espec- 

 ially of the habenae and the white mass of the pineal organ. 



B. Histology. 



I. The pineal organ {eye). The first evagination of the 

 pineal organ is composed of a layer of cells similar to ordinary 

 embryonic cells of the brain. Later the composition of the 

 superior and lateral walls shows a difference. The superior 

 wall is always composed of a single layer of cells while the lat- 

 eral have several. When the entire evagination takes the form 

 of a vesicle provided with a stalk we can clearly distinguish 3 

 different parts : The distal part of the stalk which is the fu- 

 ture nerve ; the inferior wall — the retina; and the superior 

 wall which always remains thin and occupies the place of the 

 lens. This is the "pellucida. " The nerve has at first the form 

 of a hollow stalk whose walls are composed of one layer of 

 cells. During the development the lumen is obliterated. In 

 the tissue of the stalk which has still an embryonic character 

 the white nervous mass begins to appear as nervous filaments, 

 which are developed in the stalk. In a section made near the 

 entrance of the nerve into the organ, among the numerous nu- 

 clei of the embryonic cells of the tissues of the stalk, two little 

 colorless islands were found, representing, according to our 

 author, nervous bundles. In a section taken later the nervous 

 filaments occupy almost half of the stalk. In the proximal part 

 the stalk is entirely changed into nervous filaments. The great 

 resemblance which the development of the optic nerve bears to 

 that of the pineal nerve is again confirmed by this discovery. 

 It is necessary to count the pineal nerve among the cranial 

 nerves. The numerous filaments were discovered in both trans- 

 verse and longitudinal sections. They run through the nerve, 



