280 ME. W. E. COLLIXGE ON' THE [-A-pr. 2, 



which opens by a pore over the region of the supra-davicle 

 (McMurricJi) (PL XVIII. fig. 2, x). 



2. The Main Canal commences from the point where the 

 above-mentioned branch leaves the lateral canal. It passes 

 through the frontal opening by a pore, immediately in front of 

 which the occipital commissure is given off; some little distance in 

 front of this the main canal receives the operculo-mandibular 

 branch. Its course is now directed forwards and inwards, two 

 pores opening in front of the operculo-mandibular branch. At 

 some little distance posterior to the orbit the canal divides into 

 the supra- and sub-orbital branches. 



The Sitpra-orhital Branch. — At the point of division a back- 

 wardly directed branch is given off, which passes towards the mid- 

 dorsal Hue (PI. XYIII. fig. 2) opening by pore number 12. The 

 supra-orbital branch continues forwards above the orb't, giving off 

 another branch, which also passes backwards and almost parallel to 

 the main branch ; a little distance in front of this a pore opens to 

 the surface, and the canal euters a small canal-bone, through 

 which its passes, giving off a lateral branch which meets with the 

 sub-orbital branch, thus establishing a connection between the two 

 in front of the orbit. After leaving this bone it makes a lateral 

 curve and terminates blindly at the side of the maxillary barblet. 



The Sub-orbital Branch is formed by the lower division of the 

 main canal. It passes forwards and outwards for a short distance, 

 and then makes a curve beneath the orbit, passing through the 

 infra-orbital series of canal-bones, and in the anterior region enters 

 a small canal-bone — the antorbital of some authors ; passing 

 through this it opens on the inner side and communicates with 

 the supra-orbital branch. 



The Operculo-mandibular Branch. — I have already stated that 

 this branch is connected Avith the main canal; this connection is 

 established by four small drainpipe-like canal-bones which pass 

 from the region of the posterior border of the hyomandibnlar bone 

 to the lateral border of the frontal (PI. XVIII. fig. 3, c.b.). Passing 

 from the main canal into this series of canal-bones, and through 

 the external portion of the hyomandibular bone, the canal enters the 

 preoperculum ; from here it passes into the distal portion of the quad- 

 rate and then into the mandible, opening by foiu" pores in its course. 



3. The Commissttres. — Tlie only commissure present is the 

 occipital commissure, which connects the main canal of the head 

 of either side ^^ith each other. There are two pores opening from 

 it, being situated one on either side of the iredian line. There is 

 no commissure in the anterior or frontal region. 



Innervation. 



The cranial nerves of Amiurus catus have been described by 

 Eamsay Wright (13), and I have little or nothing to add to his 

 account, excepting their relations to the sensory canal system ^. 



^ The absence of careful figures makes this otherwise excellent account very 

 diflBcult to follow, the figures on plates i. & It. being yery diagrammatic. 



