PHYSIOLOGICAL SERIES. 



The medulla is large and remarkably long, with an exten- 

 sive rhomboid fossa roofed over by a thin pleated vascular 

 membrane (turned to one side in the specimen). Within 

 the cavity certain ridges and swellings due to tracts 

 and nerve nuclei show with great clearness. A parti- 

 cularly prominent pair on either side of the mid-ventral 

 line are the fasciculi longitudinales posteriores. On the 

 outer side of these lie a pair of lesser swellings the motor 

 nuclei of the vagus ; and outside these again, on the lateral 

 walls of the ventricle, another very pronounced pair, re- 

 markable for their beaded appearance. They are the 

 sensory nuclei of the vagus. In front they pass under 

 cover of the auricles. In the swollen border of the rhom- 

 boid fossa, just before it bends to form the auricles, lie the 

 nuclei of the acusticus and lateral line (tuberculum 

 acustictim and lobus lineoe lateralis). 0. C. 1311 Ed. 



Presented by Dr. Albert GUnther. 



D. 69. The brain of a Greenland Shark (Lccmargus borealis). This 

 1 rain differs little in its essential features from that of 

 JKot'nlania. In detail the following differences are ap- 

 parent: The lamina terminals is not so deeply indented, 

 so that although the fore-brain is clearly separable into 

 unpaired posterior and paired anterior regions, the latter 

 are not so prominent. The optic lobes with their associated 

 tracts and nerves are far less developed. The cerebellum 

 i- relatively larger and extends forward to the anterior 

 border of the optic lobes. It shows upon its dorsal surface 

 a shallow transverse indentation the first indication of the 

 transverse folding so strongly marked in some of the higher 

 Elasmohranchs. 



The dorsal walls of the cerebrum and thalamencephalon 

 have been tamed to one side, exposing the cavities of these 

 part* and showing in the floor of the third ventricle a long 

 -lit leading into th infmidilniluin, saccus vasculosus, and 

 loli infVriores. The latter an; prominent and about equal 

 in rise to tin- optic lobes. The thalamoncephalon roof is 

 'i-lial and va-mlar; it is much convoluted on its inner 

 MM lace, and forms a choroid plexus that hangs within the 



