MORPHOLOGY OP TELEOSTBAN HEAD SKELETON. 503 



A Contribution to the Morphology of the Teleos- 

 tean Head Skeleton, based upon a Study of 

 the Developing Skull of the Three-spined 

 Stickleback (Gasterosteus aculeatus). 



By 



H. H. Swiiiiicrtoii, B.Sc, 



From the Zoological Laboratory, Royal College of Science, London. 



With Plates 28—31 and 5 Text Illustrations. 



Contents. 



I. iNTROBrCTOKY ..... 



n. Material and Methods 



III. Descriptive and Comparative : 



The Cranium .... 



The Visceral Skeleton 



IV. General Considerations : 



The Relation of the Trabecule to the Parachordals 



The Primordial Cranium 



The Relation of the Visceral Skeleton to the Cranium . 568 



The Systematic Position and Affinities of Gasterosteus . 574 



V. Summary and Conclusions ..... 583 



I. Inteoductoey. 



Ddeing the years which have elapsed since W. K. Parker 

 (73) published his admirable ' Monograph on the Skull of the 

 Salmon/ comparatively little has been done to advance our 



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 505 



506 

 533 



560 

 562 



