CHONDEOCEANIUM OF SYNGNATHUS FUSCUS 443 



as a core of procartilage cells, against which abut the third and 

 fourth branchial arches. 



The copula communis of a 5.7-mm. Gasterosteus has approxi- 

 mately the same relations to the hypohyals and the first and 

 second branchial arches, but in addition it has extended as 

 cartilage as far as the third branchial arch. There is also a small 

 separate cartilage between the fourth pair of branchials. The 

 independent wedge-shaped piece at the anterior end of the copula 

 communis of Gasterosteus is lacking in Syngnathus. 



The branchial cartilages of Syngnathus have not curved 

 dorsally at their distal ends in this stage as they have in the 

 5.7-mm. Gasterosteus, nor has the fifth branchial arch appeared. 

 The pharyngobranchial plates present in Gasterosteus are 

 represented in Syngnathus by a pair of procartilaginous masses 

 ventral to the parachordals and connected with each other by 

 a sheet of muscle. 



The hyoid elements are very well developed in Syngnathus. 

 The stylohyal is a small broad plate between the ventral end 

 of the hyomandibula and the dorsolateral surface of the cerato- 

 hyal (fig. 9). This element, the stylohyal, lies closely ventral 

 to the posterior margin of the hyomandibula, and not ventral 

 to its anterior margin as does the corresponding element in 

 Gasterosteus. 



The ceratohyal is very massive at this stage and extends 

 anteriorly rather than directly mesial, as in Gasterosteus. It 

 abuts against the ventrolateral margin of the elongate, hori- 

 zontal hypohyal. This latter cartilage is very peculiar in its 

 relation and extent. Instead of being a small w^edge-shaped 

 articular plate, as in Gasterosteus, it is an elongate rod of carti- 

 lage which anteriorly extends beyond the end of the ceratohyal 

 (fig. 9). The surface of articulation between the hypohyal and 

 the copula communis is nearer to the posterior end of the hypo- 

 hyal than to its anterior end. 



