442 JAMES ERNEST KINDRED 



margin of the dorsal part of the hyomandibula and the adductor 

 hyomandibiilaris muscle is inserted on its mesial face. 



Here again certain differences are to be noted between the 

 chondrocranium of Syngnathus and that of a 5.7-mm. Gastero- 

 steus. The hyomandibula of the former is more elongate and 

 rectangular on its vertical axis than is the hyomandibula of the 

 latter. The relative amount of articular surface with the otic 

 capsule is greater in Gasterosteus than in Syngnathus. The 

 ventral portion of the hyomandibula of Syngnathus is thicker 



Fig. 9 Ventral view of hyoid and branchial arches, 8-mm. Syngnathus. 

 Drawing made from wax model 230 times actual size of parts. Ratio of drawing 

 to model, 1:3. 



ABBREVIATIONS 



br.I-IV, branchial arches I to IV hyp.h., hypohyal cartilage 



C.C., copula commun.s styl.h., stylohyal cartilage 



ct.h., ceratohyal cartilage sy^n., symplectic cartilage 

 hyom., hyomandibula 



than the dorsal part, while in Gasterosteus the conditions are 

 reversed. The distinct opercular process present in Syngnathus 

 is lacking in Gasterosteus. The foramen for the passage of the 

 ramus hyomandibularis facialis is the only constant feature of 

 the body of the hyomandibula of these two forms. 



The copula communis is at this stage a delicate cylindrical 

 bar of cartilage which forms the median articulating support for 

 the hypohyal cartilages and the first and second branchial arches 

 (fig. 1, 9). It is supported in the embryonal connective tissue 

 ventral to the oral cavity (fig. 4). The cartilage is continuous 

 and of uniform caliber in its anterior part, tapering posteriorly 



