no 



'Mr. W. E. Callinge on an AhnormaUty 



XVII. — Xole on an laterestimj AhnormaUty in the Mandibular 

 Arch of Chimera nioiistiosa, L. By WAi/rER E. 

 COLLIXGE, M.Sj:., F.L.S., &c.., Research Fellow of the 

 University of 8t. Andrews, The Gatty Maiine Laboratory, 

 ISt. Andrews. 



JSoJilii little time ago, whilst examininrj: the visceral arches in 

 a specimen o£ Chinurra jnonslrosa, I met with an interesting^ 

 abnormality in the form of a small bony substance situated 

 immediately posterior to the mandibular sympiiysis. More 

 recently, in examining further examples of this Chimasroid, 

 I had the good fortune to meet with a further but somewhat 

 similar abnormality. Having failed to find any mention of 

 a like occurrence in any of the accounts of the cranial anatomy 

 of this fish, a note upon the same may not be w ithout interest. 

 lu the first specimen the abnormality consists of the 

 presence of a small plate-like bone, !iot unlike in general 



Fi?. 1. 



Outline figure of the mandible of Chimara 7nonstrosa, showiuof the 

 position of the abnormal bone. 



ah,b., abnormal bone ; g.p., grinding-plate ; La., points of attachment 

 of ligaments j »«., mandible. 



shape the urohyal of some Teleostei. It is situated imme- 

 diately behind the lower ))osterior border of the mandibular 

 symphysis, being attached to each ramus by a short strong 

 ligament (fig. 2, %.), which latter is inserted at the two 

 points marked La, in fig. 1. The bone is about 5 mm. long, 

 and readily stained with a special stain for osseous tissues. 

 Looked ;at from the ventral side, it is seen to consist of an 

 anterior triajjgular plate with a somewhat longer tail-like 

 jjurtif)n posteriorly (fig. 2), the whole being confluent with a 

 dorsal expanded jdate. in transverse section through the 

 sipterior ))ortion (fig. 2 a) the bone has the shape of a collar- 

 stud (fig. 3 a), whilst a section through the posterior part 



