CHONDROCRANIUM OF SYNGNATHUS FUSCUS 427 



.4. The neurocranium 



In the neurocranium of the 8-mm. embryo, the parts typical 

 of a teleostean neurocranium are present, but are modified 

 somewhat, foreshadowing even thus early the elongate character 

 of the adult cranium. The elongation seems to be due to a 

 precocious growth of the cartilage forming the trabecula com- 

 munis, since the distance from the anterior end of the ethmoid 

 plate to the anterior margin of the fenestra myodomus ventralis 

 is about two-thirds of the total length of the cranium (fig. 2), 

 whereas in a 25-mm. Salmo (Gaupp, '06) it is equal to one-half, 

 and in a 6.6-mm. Gasterosteus (Swinnerton, '02), to one-third 

 of the total length of the cranium. 



The anterior half of the ethmoid plate turns abruptly dorsal, 

 making a right angle with its proximal portion (fig. 1). The 

 dorsally turned part of the ethmoid is flatter in cross-section than 

 is its horizontal portion and is expanded laterally at its dorsal 

 end to form the rostral process (fig. 3). The lateral surface of 

 each side of the rostral process is grooved to receive the proximal 

 end of the palatine cartilage of that side. 



In the chondrocrania of other teleosts which have been de- 

 scribed there is no reference to a dorsal turning of the anterior 

 ethmoidal region. Swinnerton has noted a widening of the 

 ethmoid plate and its articulation wdth the palatoquadrate in 

 the 5.7-mm. Gasterosteus. The articular processes which are 

 the homologues of those in Syngnathus he named the pre- 

 ethmoid cornua. He called this type of articulation, acrartete; 

 "si palato-ethmoidal relationship in which the attachment of the 

 palatine cartilage is confined solely to the pre-ethmoid cornua. " 



A small median rostral cartilage lies on the dorsal surface of 

 the rostral process. It is attached to it by densely cellular 

 connective tissue, but otherwise is independent of the surround- 

 ing structures (figs. 1, 2, 3). The phylogenetic significance of 

 this cartilage will be considered in the description of the visceral 

 arches. 



Just posterior to the rc^tral region of the ethmoid plate, the 

 plate proper is broad and ovoid in cross-section. It is continuous 



