230 CLAP p. [Vol. XV. 



sense as in fishes," as may be easily understood when it is 

 known that 7to canals exist in tlic Ampliibia. 



Relation of Canals to Cranial Bones. 



From an examination of the skull (Fig. 4) it appears that 

 grooves or open channels in the bones serve as protection 

 for the organs. In Batrachus the only cranial bones which 

 become modified to give protection to the lateral line organs 

 are the frontal, dentary, and articular bones, the preoperculum, 

 and an accessory membrane bone in the maxillary branch of 

 the infraorbital. The curious T-shaped arrangement of the 

 upper surface of the frontal bones where the canals of the two 

 sides of the head unite, has given the specific name (tau) to 

 the species under consideration. These channels are spaces 

 between ridges of bone projecting from the surface and 

 partially surrounding the membranous tube containing the 

 sense organs. They vary in diameter in the different regions 

 of the head. In the opercular region this membranous tube 

 occupies the space (Fig. 4) between the outer edges of the 

 two lamellae of bone forming the preopercle. In the canal 

 of the maxillary branch the accessory membrane bone appears 

 .as though folded together to enclose the canal (Fig. 4, ac.b.). 

 In the mandible there is the nearest possible approach to a 

 ■closed bony canal (Fig. 5), while in the case of the temporal 

 canal there is no cranial bone involved. This short canal lies 

 outside the muscles which cover the squamosal and occipital 

 bones, and consists of a tough fibrous or semi-cartilaginous 

 covering within which is the lining epithelial layer (Fig. 22, 

 T.C.). Leydig (8) figures a similar formation in Chimaera. 

 The supporting substance is described as consisting of incom- 

 plete rings, one behind the other, comparable to the rings of 

 the trachea, and the free ends of these rings are represented 

 as branching. In cross-sections of the temporal canal in 

 Batrachus a very similar structure is seen. 



At the anterior end of the supraorbital canal there is a 

 scale-like cartilaginous formation, by means of which the canal 

 is extended across between the two openings (Fig. 22) of the 



