No. I.] THE PRIMITIVE VERTEBRATE BRAIN. 37 



Osborn, to whom I feel greatly indebted for his kindness in 

 furnishing me with everything necessary for the accomplish- 

 ment of this work, as well as for valuable advice in connection 

 with it. I also wish to express my thanks to Dr. Henry Orr 

 for the use of his sections of the Lizard. Also to Professor 

 Ryder for some fish embryos which he kindly sent me. 



The following types were studied in connection with this 

 subject, which, though not the most desirable, were the only 

 ones obtainable at the season : — 



Amphibia, Antbly stoma punctatuni. 

 Reptilia, Anolis sagroei. 

 Aves, chick embryos. 



The general object of this paper is to show that the symmet- 

 rical constrictions or folds found in the lateral walls of the 

 embryonic brain are remains of the primitive segmen- 

 tation of the neural tube, in part atavistic, extend- 

 ing into the primary fore-brain. 



Literature. — The folds in the side walls of the medulla or 

 hind-brain have been frequently noticed and commented upon, 

 but only recently has their importance as segmental structures 

 been recognized. Remak in 1850 observed these folds in the 

 medulla, and rightly considered them as structures formed in 

 connection with the "Anlagen" of the cranial nerves. They 

 were observed by Von Baerin 1828 and Dursy in 1869: the 

 latter counted six folds in the hind-brain. In 1875, Dohrn 

 pointed out the segmental significance of these folds with rela- 

 tion to the mesoblastic somites, and in the joint resemblance to 

 the segmentation of an insect embryo. In 1876, Foster and 

 Balfour, and in 1877, M ihalkovics, inclined to give a 

 mechanical explanation to these medullary folds. Beraneck 

 quite recently observed five folds in the medulla of the lizard, 

 and described and figured their connection with the origin of 

 some of the cranial nerves. Kupffer finds in the mid and 

 hind-brains of the trout and salamander at least eight segments, 

 and, if I understand him correctly, says these segments not 

 only correspond to the lateral somites (p. 476), but that there 

 is something similar to these brain segments to be observed in 

 the spinal cord. He concludes, however, by expressing the 

 opinion (p. 477) that the fore-brain is not to be reckoned in the 



