THE SKULL OF ACAXTHIAS VULGARIS 1 



GRACE A. WELLS 



TWENTY-TWO FIGURES (THREE PLATES) 



The studies for the following description of the skull of the 

 spiny dogfish of the Atlantic coast were carried on at the Uni- 

 versity of Illinois and at the Harpswell Laboratory, South 

 Harpswell, Maine, during the year 1913-1914, under the direc- 

 tion of Dr. J. S. Kingsley. 



Although the dogfish Acanthias vulgaris (often, but need- 

 lessly called Squalus acanthias) has been the subject of many 

 studies, there is as yet no adequate account of its skeleton. The 

 skull has been described in a very imperfect manner by Gegen- 

 baur ('72), but his figures are very incorrect. The development 

 of the cranium is given with some detail by Sewertzow ('99). 

 Besides, there are the laboratory directions for the study of the 

 skeleton in the publications of Pratt ('05) and Kingsley ('07). 

 Aside from these I have not found any description of the skull 

 in the literature. 



The skull of Acanthias, like that of all Selachii, is made up of 

 two distinct parts, a cranium (chondrocranium) and a visceral 

 skeleton. The chondrocranium is composed of a median brain 

 case and three lateral pairs of sense capsules, two of which — the 

 otic and the nasal — are fused with the brain ease, while the third, 

 the optic or sklera of the eye, is free. The visceral skeleton 

 consists of a series of seven arches loosely connected with the 

 cranium and surrounding the buccal and pharyngeal regions. 

 The adult cranium is without sutures or separate cartilage. 

 It can be treated as exhibiting four surfaces — dorsal, ventral, 

 lateral and basal, the latter being the face which articulates with 

 the vertebral column. 



1 Contributions from the Zoological Laboratory of the University of Illinois, 

 No. 85. 



417 



