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XV. — The Skull and Visceral Skeleton of the Greenland Shark, Lsemargus micro- 

 cephalus. By Philip J. White, M.B., Demonstrator of Zoology, University of 

 Edinburgh. Communicated by Professor Ewart. (With Two Plates.) 



(Read 15th July 1889.) 



Some time ago, at the request of Professor Ewart, I undertook an examination of 

 the skull and visceral skeleton of the Greenland shark, Lsemargus microcephalus. This 

 I readily consented to do, not only because no attempt had yet been made to describe 

 these structures in this shark, but because they claim careful consideration in view of 

 the recent work by Professor Ewart on the cranial nerves of Elasmobranchs. 



In this paper I shall endeavour, without entering into too much detail, to point out 

 some of the more salient features of the skull and visceral skeleton of Lsemargus, and to 

 compare them with those of other Elasmobranchs where that seems necessary. 



I have made preparations of the above-named structures from the heads of several 

 specimens of Lsemargus. The sharks from which the heads were taken were of various 

 sizes, the smallest being about six feet in length, and the largest twelve. As might have 

 been expected, the skeletal parts of these heads are very similar to each other, but I have 

 noticed among the few specimens I have examined points of difference, which make me 

 wish I had a larger number of preparations at my disposal, to enable me to decide the 

 more usual conditions. 



The Skull (Plate I.). 



Following the example of Gegenbaur, I shall, for purposes of description, speak of 

 the skull as consisting of four regions, viz., the occipital, the auditory,* the orbital, and 

 the ethmoidal regions. The occipital region, which is in part continuous with the 

 vertebral column, lies behind the canals for the pneumogastric nerves ; the auditory 

 extends from these canals forwards as far as the wide canals for the transmission of the 

 trigeminal and other nerves ; the orbital region, situated in front of the auditory, may 

 be said to lie between the post-orbital and pre-orbital processes ; the part of the skull in 

 front of the orbital region forms the ethmoidal region. 



The Occipital Region. 



This region, which is small compared with the other cranial regions, is in part con- 

 tinuous with the vertebral column, and lies, as above stated, behind the canals for the 



* Gegenbaur terms this — Labyrinth-Region. 

 VOL. XXXVII. PART II. (NO. 15). 2 T 



