THE SENSORY CANAL SYSTEM OF FISHES. 507 
are two irregular and unequal splints, and, like the parietals, 
do not meet in the median line. 
The dermo-ethmoid (Pl. 39, fig. 1, d. eth.) lies between 
the anterior portion of the frontals. Anteriorly it terminates 
in a long pointed process. y 
_ The circumorbital series are the canal bones which 
conduct the suborbital branch of the main canai of the head— 
after passing over the dermo-sphenotic—along the posterior 
and inferior borders of the orbit. They area series of tube-like 
bones and pass beneath the dermo-ect-ethmoid. 
The parasphenoid extends from the occipital region to 
a point slightly anterior to the nasal capsules. Its anterior 
portion is invested by two median splints—the vomers. 
The hyomandibular is a slender shaft-like bone. Its 
proximal end fits in a groove on the lateral border of the otic 
capsule. Its distal end is attached to the symplectic cartilage. 
The axis of the hyomandibular “is inclined backwards at an 
angle of less than 30° with the cranio-spinal cartilage.” 
The maxilla is a thin splint-like bone closely adherent in 
the anterior portion to the scale-like mesopterygoid and the 
surrounding cartilage ; the middle portion is separated from the 
pterygoid process by the levator mandibularis muscle, whilst 
the posterior portion adheres to the obitar process of the ptery- 
goid bar. 
The branch of the sensory canal passing along the maxilla 
is a dermal one, and does not enter into the substance of the 
bone at all. 
The mandible consists of a long dentary splint closely 
applied to the Meckelian cartilage. There is no angular element 
or os articulare. 
The mandibular branch of the sensory canal, like the 
maxillary, is a dermal one, and passes over the surface of the 
splint. 
vi. POLYODON FOLIUM. 
So far as I am aware there is no reference in any of the 
accounts of the anatomy of Polyodon to the sensory canal 
system, excepting a passing notice by van Wijhe (82). 
