ADAMS: SKULL OF THE WOLF-EEL. 341 



edge with the alisphenoid and parasphenoid ; its ventral edge 

 with the prootic, parasphenoid and hyomandibular ; posteriorly 

 with the pterotic ; dorsally with the parietal and frontal. 



Alisphenoid. (Plate XXVI, fig. 2; plate XXIX, fig. 11; plate XXXIII, 



fig. 45.) 



The alisphenoid is a thin bone, placed at the angle where 

 the parasphenoid and frontal separate posteriorly. It is tri- 

 angular in shape, with the base of the triangle placed dorsally. 

 It is less than 2 mm. in thickness, and is merely a disc of bone. 

 It has three articulations: Anteriorly with the parasphenoid 

 and frontal, these overlapping its outer face so that only about 

 one-third shows on the outside of the skull, superiorly with 

 frontal, ventrally with parasphenoid, and posteriorly with 

 sphenotic. 



Parasphenoid. (Plate XXVI, fig. 2; plate XXXII, figs. 40, 41.) 



The parasphenoid is the second largest bone in the skull, 

 the frontal being the largest. Its shape is irregular. 



Ventral Edge. 



The ventral edge is knife-like, forming a sharp keel at the 

 posterior part. Anterior to this keel the bone widens out into 

 a shallow trough or groove with thin edges, making a ventral 

 face for the articulation of the vomer. The bottom of this 

 groove is rough and has in it a smaller groove extending along 

 the whole length of the articulating surface and fitting a 

 tongue-like projection on the vomer. At the posterior end the 

 parasphenoid widens out abruptly and then rapidly narrows, 

 making a beveled surface, over which the basioccipital fits. 

 There is a deep, narrow groove in the posterior superior border 

 of the median line, and a thin tongue from the basisphenoid fits 

 into it. 

 Dorsal Edge. (Plate XXXII, fig. 41.) 



The dorsal edge is more irregular than the ventral. It ex- 

 pands and extends dorsally and outward. About one-third of 

 the dorsal edge is raised in this way. It starts to expand im- 

 mediately anterior to the articulation of the basioccipital, and 

 ends anteriorly where the upper edge dips down ventrally. 

 These expanded, up-growing wings are cut by a deep slit, 

 reaching almost to the floor of the groove between them. The 

 narrow part, posterior to this, articulates with the sphenotic, 

 and the part anterior with the alisphenoid and frontal. An- 



