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2. The Primitive Segmentation of the Vertebrate Brain. 



By Charles F. W. McClure, B.A. 

 E.M. Fellow in Biology, Princeton College, U.S.A. 



eingeg. 27. Juli 1889. 



The investigations, of which the following is a brief review of 

 Part I, were carried on in the Morphological Laboratory of Princeton 

 under the direction of Dr. Henry F. Osborn. 



The object of this paper is to show that the symmetrical constric- 

 tions or folds found in the lateral walls of the Embryonic brain are 

 remains of the primitive segmentation of the neural tube, 

 in part atavistic, extending into the primary fore brain. 



The following types were studied: Amphibia. Ambly stoma punc- 

 iatum\ Reptilia, Anolis sagroei; also chick embryos. 



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 vonBaer'^ in 1828 andDursy^in 

 1869; the latter counted six folds in the hind brain. In 1875, Dohrn* 

 pointed out the segmental significance of these folds with relation to 

 the mesoblastic somites, and in the joint resemblance to the segmen- 

 tation of an insect embryo. In 1876, Foster and Balfour^, and in 

 1877, Mihalkovics^ inclined to give a mechanical explanation to 

 these medullary folds. Béraneck" quite recently observed 5 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 



1 Untersuchungen über die Entwicklung der Wirbelthiere. Berlin, 1850 — 1855. 

 §28. 



2 Entwicklungsgeschichte der Thiere. I. Th. p. 64. 



3 Entwicklungsgeschichte des Kopfes. Tübingen, 1869. Atlas, Taf. Ill Fig. 15. 

 * Der Ursprung der Wirbelthiere und das Princip des Functionswechsels. 



Leipzig, 1875. p. 1. 



5 Grundzüge der Entwicklungsgeschichte der Thiere. Aus dem Englischen 

 übersetzt von N. Kleinenberg. Leipzig, 1876. 



6 Entwicklungsgeschichte des Gehirns. Nach Untersuchungen an höheren 

 Wirbelthieren und dem Menschen. 



■^ E. Béraneck, Recherches sur le développement des nerfs eraniaux chez les 

 Lézards. Recueil Zoologique suisse. T. I. p. 557. 



8 C. Kupffer, Primäre Metamerie des Neuralrohrs der Vertebraten. Sitzung 

 der math.-phys. Classe (Akad. München) vom 5. December 1885. 



