— 8 — 



TEMPORAL FOSSA. 



The temporal fossa of fishes is a hole formed by the more or less complete roofing, by dermal 

 bones, of the temporal groove on the dorsal surface of the primordial cranium. This fossa and groove 

 are both shown in what is considered as the most primitive condition known, in Amia calva, in which 

 fish they have both been described by Sagemehl ('83); but Sagemehl did not recognize, in this fish, 

 an anterior extension, or diverticulum of the groove, to which I later called attention ('89, p. 501), 

 and which becomes incorporated in the groove and fossa in certain other fishes, as shown below. 



In Scorpaena scrofa the temporal groove is deep, but short, antero-posteriorly, as compared 

 with that of Scomber, corresponding only to the deeper, posterior portion of my descriptions of the 

 groove in the latter fish. The groove is, in Scorpaena, completely roofed, mainly by the lateral extra- 

 scapular and suprascapular bones; but there are, along theedges of the groove, overhanging portions of 

 the pterotic, epiotic and parieto-extrascapular, and between the edges of the parieto-extrascapular and 

 lateral extrascapular, there are narrow spaces spanned by tough fibrous tissue. The groove being 

 completely roofed, becomes a fossa, and opens onto the posterior surface of the skull by a large opening 

 which occupies the dorso-lateral portion of that surface. A small opening between the hind edge of 

 the pterotic and the opisthotic process of the suprascapular, leads into the fossa from the lateral 

 surface of the skull, and through this opening the supratemporal branch of the nervus lineae lateralis, 

 accompanied by certain vagus fibres, passes inward into the fossa. The mesial wall of the fossa is 

 formed by the epiotic; its lateral wall by the pterotic, the opisthotic, and the opisthotic process of 

 the suprascapular. Its floor is formed in part by the sloping side walls of the pterotic and epiotic, 

 but mainly by a relatively wide strip of cartilage which separates those two bones, and which is the 

 temporal interspace of my descriptions of Scomber. Posteriorly this interspace of cartilage is bounded 

 by the dorsal edge of the exoccipital, which bone forms the floor of the posterior opening of the fossa, 

 and, in large specimens, a small part also of the floor of the fossa itself. 



The fossa lodges, as in other fishes, an anterior extension of the trunk muscles, and if those 

 muscles were to push forward and upward, through the space covered by the lateral extrascapular, 

 onto the dorsal surface of the skull , they would push forward dorsal to the parietal portion of the 

 parieto-extrascajDular and dorsal also to the depressed hind edge of the frontal, and, occupying the 

 region between the mesial and lateral rows of spines, would give rise to the temporal groove of Scomber. 



In one specimen, in which the parieto-extrascapular had been removed from the underlying 

 bones, the dorso-anterior end of the temporal groove formed a sort of pocket which is apparently 

 the homologue of the recess in the antero-lateral corner of the groove in Scomber ('Allis, '03, p. 51), 

 and the homologue also of the anterior diverticulum of the groove in Amia. The pocket, in Scor- 

 paena , opened onto the dorsal surface of the primordial cranium by a small and separate opening, 

 which lay immediately anterior to the suturating edges of the superficial portions of the epiotic and 

 auto-pterotic, between those bones and a portion of the chondrocranium, and was covered externally 

 by the parieto-extrascapular. 



In the Elopidae and Albulidae, the former of which are said by Ridewood ('04a) to be the most 

 archaic of existing teleosts, and the latter to be in but few respects more highly specialized, the tem- 

 poral fossa is said to be very extensive. Ridewood calls this fossa the posterior temporal fossa, and 

 says that it extends forward a considerable distance beneath the frontal; apparently extending even 



