576 H. H. SWINNEHTON. 



basioccipital partially, from the pro-otic. In Gasterosteus the 

 space just referred to is represented by aii area of cartilage 

 (PI. 29, fig. 21). In the s))heDoidal region of Fistularia 

 the pro-otic completely encloses the foramen for the exit 

 of part of the fifth nerve, and forms the hinder boundary 

 of the other exit. The large alisphenoid forms the front 

 boundary for the rest. No eye-muscle canal is present, 

 consequently the parasphenoid lies flat against tlie floor of 

 the cranium. Laterally it sends out processes up to the 

 sphenotic. In Syngnathus McMurrich was doubtful about 

 the presence of an alisphenoid, but the enclosure of the tri- 

 geminal nerve exit by the pro-otic, and the abseuce of the 

 eye-muscle canal, furnish points of resemblance to Fistularia; 

 whilst in the union of parasphenoid and frontal processes it 

 is similar to Gasterosteus. 



Thus the last named is more normal in the occipital region 

 and more advanced in the sphenoidal than the other two, and, 

 on the whole, dilfers more from them both than they do from 

 one another. 



In the anterior portion of the cranium, Fistularia and 

 Syngnathus present the same features as those given above 

 for the Gasterosteus, but it is greatly elongated, and almost 

 completely ossified. In the first this region is propor- 

 tionally much wider, because the narrow pre-ethmoid is 

 supplemented laterally by the nasals. Apart from this, and 

 the presence of teeth on the vomer, it bears a much closer 

 resemblance to the second than to the last, for though 

 Gasterosteus spinachia has an elongated ethmoid, this is 

 still almost wholly cartilaginous. 



In the visceral skeleton all are alike in the tendency 

 towards a weakening of the branchial apparatus, in the great 

 forward slant of the liyomandibular, in the great elongation 

 of the symplectic, in the great reduction or complete sup- 

 pression of the metapterygoid cartilage, in the absence of an 

 ectopterygoid, and in the possession of the acrartete condition. 



In Fistularia the reduction of the branchial skeleton has 

 advanced much further than in Syngnathus, for all the basi- 



