Zool.— Vol. I.] STARKS-SEBASTOLOBUS. 363 



The myodome, or chamber for the insertion of the rectus 

 muscles of the eye, is partitioned off from the brain cavity 

 by shelves of bone developed from the inner surfaces of the 

 prootics, which meet medially and form the base of the 

 brain cavity {basis cranii). The partition is continuous with 

 the basioccipital, which is concave along its lower surface, 

 leaving a tube between it and the parasphenoid. It opens 

 to the exterior as a very small pore in a notch in the end of 

 the parasphenoid. 



The basisphenoid (bs.) articulates to the roof of the myo- 

 dome by two lateral limbs, leaving a small space behind it. 

 It extends forward and downward nearly to the para- 

 sphenoid as a thin paddle-shaped bone. 



The parasphenoid {fas.) sends a brace upward from each 

 side along the anterior edge of the prootic. It runs back as 

 a splint-like bone nearly to the posterior end of the basi- 

 occipital. 



The frontals {fr.) are tunnelled longitudinally for their 

 whole length by large sensory canals.* They bear three 

 pairs of spines on their lateral edges. 



Lying laterally to the frontals and the ethmoid is the -pre- 

 frontal (f>f), whose upper end projects upward as a spine. 



In the sphenotic {spo.) is a continuation of the orbital 

 sensory canal. On the lower surface is sunk a socket for 

 the insertion of a projecting limb from the anterior part of 

 the head of the hyomandibular. 



The prootic {pro.), alisphenoid {als.), ethmoid {e.), and 

 vomer {v.) are sufficiently shown in the drawings and need 

 no description. 



II. — Suspensorium, Mandible, and Opercular 



Apparatus. 



Plate XXII, Fig. 4. 



The hyomandibular {hm.) articulates with the sphenotic 

 by a rounded process from its upper anterior edge, behind 



*Prof. C. W. Greene of Stanford University has protested to me against 

 the use of the term "mucous canal." He has proved in many instances 

 that, though they may be filled with mucous, their function is essentially that 

 of sensory canals and they should be so called. 



