168 



SCIEJSrCE. 



[Vol. VIII., No. 185 



wards to the olfactory lobes, the smaller passing 

 backwards. They correspond in distribution to the 

 two divisions of the anterior commissure in the mam- 

 mal. Does the upper bundle, then, represent the 

 corpus callosum ? When we follow the distribution 



V — cal 



Pig. 3. — Transverse section of the fore-brain of the turtle 

 in the plane of the cerebral commisures. 



of its fibres to the upper inner cell-area of the hem- 

 ispheres, this question seems clearly answered in the 

 affirmative. But here arises a difficulty ; this bundle 

 Jies below the foramen of Monro, and its fibres pass 

 upwards behind the foramen, and then forwards 

 above it. This is exactly the reverse of their posi- 

 tion in the mammalian brain ; but an explanation is 

 found in the fact that the frog's brain retains many 

 fish characters, and, among them, a large ventricle 

 (the ventriculus communis) common to the two hemi- 

 spheres, with the cerebral commissures lying in its 

 floor. The brain of the turtle gives us a step nearer 

 the mammalian type ; for here, as in the mammal, 

 the cerebral commissures lie in the front wall of the 

 common ventricle, and the callosal bundle passes 

 upwards in front of the foramen of Monro, and its 

 fibres spread like rays over the entire inner wall of 

 the hemispheres. Eemoving all further doubt that 

 this bundle is homologous with the corpus callosum, 

 is the fact that connected with it, as in the mam- 

 mals' brain, are fibres passing backwards and down- 

 wards into a region which corresponds with the 



Fig. 4. — A vertical section of the brain of the duck {Anas 

 boschas). 



mammalian hippocampus. These fibres are usually 

 described as the commissural portion of the fornix. 

 The snake's brain (Tropidonotus) gives us a higher 

 step, for, although the corpus callosum is a less dis- 

 tinct bundle, fibres are observed descending in the 

 lamina terminalis, which in their relations closely re- 

 semble the columns of the fornix, — another struc- 

 ture which has been supposed to be peculiar to the 

 mammals. In this brain also the olfactory and tem- 

 poral divisions of the lower bundle have precisely the 



same relations as in the mammalian anterior commis- 

 sure, demonstrating beyond a doubt that the lower 

 bundle represents the entire anterior commissure, 

 and not merely its temper U division, as Stieda and 

 Mihalkovics contend. Upon drawing apart the 

 hemispheres of the freshly removed brain of a duck, 

 we observe a delicate thread of fibres slightly above 

 a large and distinct lower commissure. The former, 

 in transverse section (fig. 5), is seen passing directly 

 upwards into the inner wall of the hemispheres, and 

 below it is a powerful transverse commissure. We 

 cannot fail to recognize that these two bundles are 

 essentially similar in distribution and position to 

 those in the turtle, and that the upper one is a rudi- 

 ment of the corpus callosum. 



Here is seen an apparent anomaly. In the frog's 

 brain, the proportion of the corpus callosum to the 

 anterior commissure is as 2 to 1 ; in the turtle it is 

 about 5 to 4, while in the biids it is about 1 to 6. 

 Thus, with an ascending scale of intelligence, we 

 find a diminishing corpus callosum, a relation the re- 

 verse of that which obtains in the mammals. The 



4^Zv 



cah 



Fig. 5. — a transverse section of the duck's brain through 

 the commissures. 



explanation of this is probably that in the Sauropsida 

 generally the inner wall of the hemispheres is thin, 

 and in the birds it is reduced to a mere sheet of nerve- 

 tissue, and this reduction of distribution area has 

 effected a reduction of the commissure. In all these 

 animals the united commissures are even smaller in 

 proportion to the hemispheres than they are in the 

 monotremes. Henry F. Osborn. 



A brilliant meteor. 



You may think worthy to record the following 

 memoranda of an unusually large and brilliant meteor, 

 reported by Mr. E. Stockin of Watertown, Mass., 

 and seen from that place on Sunday evening, Aug. 

 8. Time, about 8.45 p. m. Direction, north-east to 

 east. The attention of both Mr. and Mrs. Stockin 

 was first called to the meteor by the flash, which il- 

 luminated surrounding objects. On turning, they 

 saw the meteor, apparently about thirty degrees 

 above the horizon. It was of a bright red color, of 

 about one-fourth the size of the moon, occupying five 

 or six seconds in its descent, disappearing behind 

 some buildings while still brilliant, and leaving a trail 

 of brilliantly colored sparks, and subsequently a 

 white streak visible some seconds. The exact direc- 

 tion of the meteor from the observer could be ascer- 

 tained, if desirable, by means of positions noted at 

 the time. C. H. Ames. 



Boston, Mass. 



