766 EEPORT OF COMMISSIONER OF FISH AND FISHERIES. [20] 



for the exit of the glossopharyngeus; anteriorly by the postorbital pro- 

 cess and the posterior circumference of the orbit. 



It forms the greater part of the lateral wall of the skull situated be- 

 hind the orbits and includes the ossified petrosal and postfrontal. 



The petrosal (Plate I, Figs. 2 and 3, Fe) is nearly circular in form, be- 

 ing connected behind and above by a small part of its periphery to the 

 intercalare in a serrate suture. 



It is separated from the surrounding bones by broad areas of carti- 

 lage, from the basioccipital posteriorly, the squamosal laterally and 

 above, the postfrontal above and anteriorly, from the alisphenoid ante- 

 riorly, and from the petrosal of the opposite side by a mesial band of 

 the same material. 



Above the petrosal we find the long, flat, and longitudinally placed 

 facet of articulation for the hyomandibular (Plate I, Figs. 2 and 3 hm.). 

 This facet is entirely in cartilage, with the exception of the postero- 

 superior angle, which is slightly overlapped by a thin piece of the squa- 

 mosal. 



Anteriorly and above the petrosal lies the ossified postorbital process 

 — the postfrontal (Plate I, Figs. 2 and 3, Psf.). This bone has the form 

 of a triangular pyramid, whose apex is directed laterally and upward. 

 The superior aspect of this bone, which is stamped with all the characters 

 of a dermal bone, has already been thoroughly described; of the two re- 

 maining sides, one faces oiftward and the other assists in forming the 

 hinder part of the upper margin of the orbit. The ossification of the 

 postfrontal does not reach through the entire thickness of the lateral 

 cartilaginous skull wall, but remains separated from the brain cavity at 

 all points by cartilage. J^ow, at the dividing line between the bone and 

 the cartilage there lies a canal that commences at the lower margin of 

 the bone at the side of the skull and makes its exit at the anterior angle 

 of the temporal fossa. So far as I could satisfy myself, it contains ves- 

 sels intended for the soft parts contained in the temporal fossa. This 

 canal has no greater morphological significance, and I only mention it 

 for the sake of making my description complete. Two openings are 

 formed near the anterior margin of the petrosal ; the upper and larger 

 one is for the facial nerve and jugular vein (Plate I, Figs. 2 and Sfa.), 

 the smaller and lower one for the carotid (Plate I, Fig. 3m.). While 

 still in the brain case the facial nerve gives off" a branch which, running 

 forward, enters the orbit at the posterior margin of the fenestra — to be 

 spoken of further on — thence traversing the lower lateral margin of 

 this cavity, to be distributed to the mucous membrane of the mouth. 



This branch of the facial, which universally occurs in the Teleosteans, 

 has always been referred to as the homologue of the ramus palatinus 

 of the Selachians. If one considers that the ramus palatinus of the 

 Selachians always arises extracranial from the facial, and from this ori- 

 gin runs anteriorly, while the nerve bearing the same name in Amia and 

 bony fishes has an intracranial origin, the .question of their homology 



