CHONDROCRANIUM OF SYNGNATHUS FUSCUS 447 



lages of Syngnathus are to be regarded as remnants of the 

 olfactory capsules, the condition of the ectethmoids in the above 

 forms indicates a more specialized relation. Therefore, I am 

 regarding the relation of the ectethmoid cartilages of Syngnathus 

 as primitive. 



There is no tegmen or cartilage dorsal to the brain in the 

 ethmoid region, the tips of the frontal ossifications appearing 

 as a pair of delicately spined osseous lamellae in the fibrous 

 connective tissue enclosing the brain. 



Just posterior to the ectethmoid region the oblique eye muscles 

 have their origin in the fibrous tissue of the interorbital septum 

 and are not related to the cartilage of either the ethmoid plate 

 or the ectethmoid cartilages. The trabecula communis is flatter 

 and broader in cross-section than that part of the ethmoid plate 

 immediately ventral to the ectethmoid arch, but it gradually 

 diminishes, until at the anterior margin of the fenestra myodomus 

 ventralis it is a very slender cylindrical bar. The parasphenoid 

 lamella is attached to its ventral surface by connective tissue. 



In the region of the anterior margin of the fenestra myodomus 

 ventralis, the internal carotid arteries, which more anteriorly 

 were dorsal to the trabecula communis, now pass ventrally into 

 the space between the trabeculae cranii (fig. 13). The recti 

 eye muscles enter the fenestra myodomus ventralis dorsal to 

 the internal carotid arteries between the trabeculae cranii and 

 the fibrous connective tissue enclosing the brain. The hypo- 

 physis cerebri lies posterior to this region, so that, in accordance 

 with Allis' criteria, this space between the anterior ends of the 

 trabeculae cranii has been termed the fenestra myodomus 

 ventralis, and not the fenestra hypophyseos. As in the younger 

 stage, the parasphenoid ossification forms the floor of the fenestra 

 myodomus ventralis and serves as a surface of attachment for 

 the recti muscles. The anterior end of the hypophysis cerebri 

 appears just posterior to this region, and the space occupied 

 more anteriorly by the recti muscles and by the carotids is 

 obliterated, the hypophysis pushing the meningeal tissue against 

 the trabeculae cranii. This portion of the intertrabecular 

 fenestra may be properly termed the fenestra hypophyseos. 



