— 104 — 



and it projects ventro-mesially into the cranial cavity of the prepared skull and terminates witli 

 a free edge. 



The bind edges of the two legs of the alisphenoid are in contact with the anterior edges of 

 corresponding plates of bona on the ventral edge of the orbital portion of the proötic; and these two 

 plates of this part of the proötic may for convenience be called the parasphenoid and basisphenoid 

 legs of the orbital part of that bone. The basisphenoid leg corresponds to that part of the external 

 surface of the proötic of Scorpaena that forms the mesial wall of the jugular groove on the orbital 

 surface of the bone; the parasphenoid leg corresponding to the membrane that spans that groove 

 and was referred to, when describing Scorpaena, as a membranous anterior extension of the lateral 

 wall of the trigemino-facialis chamber. This membrane having ossified, in Cottus, as part of the 

 proötic, the jugular groove of Scorpaena becomes, in Cottus, a canal which opens anteriorly into the 

 cranial cavity, while posteriorly it opens by a foramen-like opening onto the external surface of the 

 proötic. The anterior end of the canal is much larger than its posterior end, and the canal is con- 

 tinuous anteriorly with the V-shaped space between the two legs of the alisphenoid, the two spaces 

 together forming a recess in the cranial cavity which may be called the internal jugular recess. The 

 internal jugular vein and the truncus ciliaris profundi enter this recess at its anterior end, and, running 

 posteriorly, issue through the foramen-like opening at its bind end. This latter foramen is accordingly 

 an internal jugular foramen, but it is not the strict homologue of the foramen that I have described 

 as the internal jugular foramen in one specimen of Scorpaena; for the foramen in Cottus is bounded 

 by the proötic and the parasphenoid alone, while in Scorpaena it is bounded by the alisphenoid, 

 the proötic and the parasphenoid. The foramina in the two fishes result, however, from the 

 bridging of one and the same canal by a bridge of bone that is narrow in one fish and wide in 

 the other. 



On the internal surface of the alisphenoid of Cottus, there is, as in Scorpaena, a brace-like 

 flange, which lies between the fore-brain and mid-brain recesses of the cranial cavity. In Cottus 

 this flange is thin and tall and forms, with a corresponding flange on the ventral surface of the frontal, 

 a somewhat important partition between the dorsal corners of the two recesses. 



The alisphenoid is perforated, in its antero-ventral portion, by a foramen which varies consi- 

 derably in position in my specimens. It transmits the lateralis nerve destined to innervate the 6th. 

 or terminal organ of the supraorbital canal, the nerve always being accompanied by a blood vessel. 

 Whether other than lateralis fibers form part of the nerve was not investigated. The nervus troch- 

 learis passes across the free edge of the alisphenoid without perforating it. 



The SPHE NÖTIG is normal in position and forms, as usual, the dorsal portion of the facet 

 for the anterior articular head of the hyomandibular and the anterior portion of the dilatator fossa. 

 The oticus canal enters the bone on its orbital surface, and traversing the bone opens into the bottom 

 of the dilatator fossa. A flange on the cerebral surface of the bone forms part of the anterior bounding 

 wall of the labyrinth recess. The dorsal surface of the bone is almost entirely covered by the frontal 

 and pterotic, comes nowhere to the level of the dorsal surface of the skull, and gives suj^port to a 

 part only of the dorsal edge of the postfrontal. 



The PROÖTIC differs in certain important respects from the bone in Scorpaena and Sebastes. 

 One of these differences is the enclosing of the internal jugular groove, and has just above been de- 

 scribed. The other relates to the trigemino-facialis chamber, and is described below. The bone is- 



