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S u m m a r y. 



1. The mesethinoid processes of fishes are processes of the mesethmoid bone, or of the 

 ethmoid cartilage, that give origin to the ethmo-maxillary ligament, and that support or give 

 attachment to the hind end of the nasal of either side. In the Loricati they are prominent processes 

 of the mesethmoid; in Trigla and Peristedion they are small processes of the same bone, wholly 

 concealed beneath the nasals; while in Dactylopterus they are small processes of the ethmoid 

 cartilage. 



2. The dilatator, temporal and supratemporal fossae of fishes are grooves on the dorsal surface 

 of the primary cranium, more or less completely roofed by dermal bones. Each of these grooves may 

 have an anterior extension that lies lipon the outer surface of the dermal bones of the roof of the skull, 

 as in Scomber. In the mail-cheeked fishes, these anterior extensions are not found, but the areas 

 occupied by them in Scomber are represented, on either side of the dorsal surface of the skull of the 

 Loricati, by contiguous regions bounded by four more or less developed ridges that radiate approx- 

 imately from the frontal spine. The ridge between the anterior extensions of the temporal and 

 supratemporal fossae is in a measure continuous with the epiotic ridge on the posterior surface of 

 the skull, and the posterior semicircular canal lies internal to this latter ridge. The ridge between 

 the anterior extensions of the temporal and dilatator fossae is similarly continuous with the ridge 

 that forms the boundary between the posterior and lateral surfaces of the skull, and the posterior 

 leg of the external semicircular canal lies internal to a portion of this ridge. The ridge forming 

 the anterior boundary of the anterior extension of the dilatator fossa is approximately continuous 

 with the ridge that separates the hind wall of the orbit from the lateral surface of the brain case, 

 and the summit of the anterior semicircular canal lies in a measure internal to it. The position 

 of the frontal spine, from which these several ridges radiate, corresponds somewhat to that of the 

 opening of the endolymphatic tube in selachians. The subtemporal fossa, on the lateral surface 

 of the skull, lies between the external semicircular canal and the utriculus. 



The temporal fossa may have an epiotic diverticulum, and it may also have, as in Amia, an 

 anterior diverticulum. This latter diverticulum lies on the dorsal surface of the primary cranium, 

 beneath the dermal bones of the roof of the skull, and in certain fishes (Elops, Albula) it becomes a 

 large and important portion of the fossa. But this anterior diverticulum of the fossa is not to be 

 confounded with the anterior extension just above referred to, the former lying ventral and the latter 

 dorsal to the dermal bones. 



The anterior extensions of the supratemporal grooves have coalesced in the Loricati to form 

 the subquadrangular groove on the vertex. 



3. The premaxillary of the mail-cheeked fishes has, on its anterior end, two processes, one of 

 which is the ascending process properly so-called, and the other an articular process; but the two 

 processes together are usually referred to as the ascending process of the bone. 



The articular process is probably the earlier acquisition of the two, is apparently fouud in 

 all osseous fishes, and it, alone, is sometimes miscalled the ascending process of the bone (Amia. 

 Salmo). 



The ascending process is formed by the fusion with the premaxillary of a supraethmoid bone, 

 the latter bone being primarily developed in protective relation to a line of latero-sensory organs, 

 and being so found, not only in certain ganoids (Amia, Polypterus) but also in Elops and probably 



