372 Johi^ F. Holm 



gaugliou wbicli is considered most probably bomologous witb tbe 

 »Ganglion babeuulae« but wbich be tbinks could possibly be equal 

 to tbe Tori longitudiualis of tbe Teleostei. Bebind tbe Tubercula 

 intermedia and separated from tbem by a deeper depression and a 

 central pit, anotber pair of tuberosities are found situated in a cor- 

 responding position to tbe Corpora bigemina and are embraced la- 

 terally by a pair of converging processes going in a backward 

 direction; these belong to tbe Medulla oblongata and represent tbe 

 Corpora restiformia. He recognises tbe entire absence of the Cere- 

 bellum. 



In describing the divisions in tbe brain of Myxine I use tbe 

 terminology adopted in Quain's Anatomy, part I and not that for 

 our object unnecessaril}^ complicated one invented by His, which is 

 contained in his »Nomina Anatomica«. 



Olfactory region and Thalamencephalon. 



If we look at a horizontal section through the brain of Myxine, 

 taken close to the dorsal surface. Fig. 5, we find rostrally a conglo- 

 meration of olfactory glomeruli, the Stratum glomerulorum, in close 

 contact posteriorly to a layer of gray matter consisting of small 

 nerve cells. This area corresponds to the first division of tbe brain, 

 the gray matter being homologous to the Stratum griseum, the whole 

 division being all that exists of the Prosencephalon. Further cau- 

 dally a group of cell nuclei appear which belong to the next division 

 of the brain, called by Sanders »tbe Cerebrum«, by Retzius »Vor- 

 derbirn«. This part of the brain contains the third ventricle, the 

 hypophysis, in its caudal end the Ganglion babenulae are situated, 

 the cell nuclei correspond to tbe optic tbalami and the whole divi- 

 sion to tbe Thalamencephalon. The next two divisions belong to 

 the Mesencephalon and have one pair of cell nuclei each, the rostral 

 pair corresponding to tbe Nucleus praetectalis and tbe posterior to 

 the Corpus quadrigeminum posterius. 



Tbe researches of Dean (6) on the development of Bdellostoma 

 seem to confirm tbe oi)inion that both divisions should be considered 

 as belonging to the Mesencephalon, as he states that »In tbe matter 

 of the topography of the brain, the most extraordinary character is 

 easily tbe great length of what is provisionally regarded as tbe 

 mid-brain«. 



From the bottom of the median grove and between the Tbalam- 



