288 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



process passes forward and upward to touch upon the alisphenoid. 

 Upon the inner surface of the bone, not far from the base of this 

 process, is a foramen leading into a canal which traverses the 

 hyomandibular from above downwards and backwards, opening on its 

 posterior surface a little above the posterior inferior angle. This 

 canal contains the R. hyoideo-mandibularis facialis. On the outer 

 surface is a flattened ridge overlying this canal, immediately behind 

 which is the articular knob for the operculum, and extending forward 

 at right angle to it is a ridge for the attachment of muscles. The 

 hyomandibular articulates above with the pterotic, sphenotic, and 

 alisphenoid ; in front with the metapterygoid, and slightly with the 

 quadrate ; below with the symplectic cartilage and the preoperculum ; 

 and behind with the operculum. 



2. The Symplectic 



Element does not appear to ossify. It is represented by a cartilage 

 contained partly within the hyomandibular and partly within the 

 quadrate, and filling up the space between these two bones. 



3. The Hyoid 



May be described as consisting of five portions, as follows : — 



(a) The interhyal is represented by a small knob at the extremity 



of the ai'ch which is connected by ligament to the inter- and preoper- 



culum, the hyoid thus being fixed at its upper extremities without 



articulation with the symplectic. 



lb) The epihyal is the upper triangular portion of the arch, 



separated from the succeeding portion by a deep notch above and 



below and by a \xsually well marked articulation. 



(c) The ceratohycd is the longest portion of the arch ; broad and 

 flat above, it becomes contracted towards its anterior extremity and 

 again expands for articulation with the hypohyals. Both the cerato- 

 hyal and epihyal bear branchiostegal rays on their lower borders. 



(d) The hypohyal is united with its fellow of the opposite side by 

 ligament. The bone so denominated in Amiurus is not simple, but has 

 usually connected with it one or two accessory nodular bones, the 

 number frequently varying on opposite sides in the same individual. 



(e) The urohyal is an impair bone extending back from the junc- 

 tion of the hypohyals. Anteriorly it is partly divided into two 

 rounded portions, from the extremities of each of which a ligament 

 passes forward uniting it to the hypohyal. Behind is a thin flattened 



