AlE-BLADDEE IN NOTOPTERUS BOENEENSIS. 517 



Two longitudinal grooves traverse the lateral portions of the 

 cranial roof, and are bounded for the anterior part of their 

 extent by prominent bouy ridges on the external surface of the 

 frontals, and more posteriorly by similar parallel ridges on the 

 upper surface of the pterotic (PI. 37. figs. 4 & 6, g). Externally,, 

 the grooves are closed in and converted into complete canals by 

 the thin, scaleless, superficial skin of the dorsal surface of the 

 head. In these grooves or canals are lodged the main lateral 

 sensory canals of the head and their respective supra-orbital 

 prolongations. At its hinder extremity each groove suddenly 

 deepens into a shallow basin-shaped, or funnel-like, oval de- 

 pression, at the bottom of which is the somewhat smaller, 

 but also oval, cranial fontanelle (PI. 37. fig. 6, c.f.), which in 

 the dried skull communicates internally with the cavity of the 

 auditory capsule, precisely as described by Cuvier and Valen- 

 ciennes. The margins and sides of the funnel are smooth and 

 rounded, and are formed anteriorly, and also to a large extent 

 on each side, by the deeply concave posterior border of the 

 pterotic {pt.), and completed laterally and behind by i;he epiotic 

 (ep.), the opisthotic {pp.), and the exoccipital (eo.). The long 

 axis of the mouth of the funnel measured 10 mm., and its trans- 

 verse dimension 6 mm. The fontanelle is smaller, the cor- 

 responding dimensions being 6 mm. and 4 mm. respectively. 

 Across the fontanelle, and firmly attached to its margins, is 

 stretched a thin, fibrous, drum-head-like membrane, which 

 is in relation internally with the somewhat fatty perilymphatic 

 tissue of the interior of the auditory capsule. 



There is, however, one point to which Cuvier and Valenciennes 

 make no reference, viz. — the relations of the main sensory 

 canal of the head to the cranial fontanelle and the mem- 

 brane closing it. As it passes directly dorsad to the pi'oximal 

 or supra- clavicular element of the pectoral girdle, the sensory 

 canal traverses the axis of a somewhat cylindrical bone, and 

 then enters the lateral longitudinal groove or canal to whicli 

 reference has just been made. At this point the sensory canal 

 expands considerably, and assumes a singular cavernous or sinus- 

 like appearance, practically filling the bony groove in which it is 

 lodged. The lateral and inner walls of the sensory canal are 

 here strengthened by two longitudinally-arranged, thin, demi- 

 cylindrical bones, or sensory canal ossicles, the convex inner 

 surfaces of which are in close relation with the cranial fontanelle 



LINN. JOUEN. — ZOOLOeX, VOL. XXTII. 39 



