CHONDROCRANIUM OF SYNGNATHUS FUSCUS 433 



trabecula cranii and the postorbital process of that side. Swin- 

 nerton indicates this relation of the trigeminal ganglion to the 

 trabecula and the postorbital process in Gasterosteus. Gaupp 

 calls this space in a 25-mm. Salmo the incisivum prooticum. 



Farther posterior, the prootic process of each side abuts against 

 the lateral surface of the trabecula cranii (figs. 1, 2). The 

 cartilage forming each of these structures retains its identity at 

 the point of union. The perichondria of the two cartilages form 

 the line of separation between them. In this immediate region 

 the trabeculae are flatter and more ovoid than they are more 

 anteriorly. This is probably the region of junction between the 

 trabeculae and the parachordal cartilages (fig. 6). 



A wide space, such as is found between the trabeculae cranii 

 and the ventral surface of the brain in the fenestra myodomus 

 ventralis region, is obliterated here by the presence of the 

 hypophysis cerebri, so that the membrane enclosing th^ brain 

 is continuous with the perichondria of the trabeculae cranii 

 (fig. 6). 



A foramen is present in the cranial wall just posterior to the 

 prootic process. Through this foramen the jugular vein and 

 the ramus hyomandibularis facialis pass (fig. 6). The posterior 

 margin of the foramen is formed by the wall of the otic capsule. 



Posterior to the facialis foramen the parachordal cartilages 

 are fused with the ventromesial margins of the otic capsules. 

 Mesially, the parachordals are closer together than were the 

 trabeculae farther anterior. The parasphenoid lamella forms 

 the floor of the intervening fenestra, its roof is formed by fibrous 

 connective tissue ventral to the posterior end of the hypophysis. 



Just posterior to this region the parasphenoid ends and the 

 space between the parachordals is occupied by the anterior end 

 of the notochord (fig. 7). The notochord is separated dorsally 

 from the cavum cranii by connective-tissue stroma connecting 

 the perichondria of the parachordals. The space between the 

 parachordals in which the notochord lies has been called the inter- 

 parachordal fossa in Gasterosteus (Swinnerton) , and the fenestra 

 basicranii posterius in Salmo (Gaupp) ; the latter terminology is 

 used in this paper. 



