ON THE OTIC REGION OF LEPIDOSTEUS. 245 



15. On certain Features o£ the Otic Region of the Chon- 

 drocraninm of Lepidosteus, and Comparison with 

 other Fishes and Higher Vertebrates. By Edward 

 Phelps Allis, Jr., F.Z.S. 



[Received May 6, 1919 : Read May 27, 1919.] 



In a figure of a 149 mm. specimen of Lepidosteus osseus, Veit 

 ('07) shows the Larger part of the clorso-lateral edge of the otic 

 :portiou of the chonclrocrauium formed by a laterally projecting 

 ridge which he says is currently called the crista parotica, and 

 he adopts this name for it. It will, however, be later shown 

 that the anterior portion of this ridge is not included in the 

 crista parotica of current descriptions of mammalian embryos, 

 and there is some doubt as to any part of it being the strict 

 homologue of that crista. The name is therefore inappropriate, 

 and as the ridge lies, in fishes, in part on the sphenotic and in 

 part on the pterotic portion of the chondrocranium, I shall call it 

 the spheno-pterotic ridge. 



The sphenotic portion of this spheno-pterotic ridge is formed, 

 in Veit's 149 mm. specimen oi Lejndosteus, by the dorso-lateral 

 edge of the autosphenotic, and it begins, anteriorly, at the 

 summit of the postorbital process. Its pterotic portioia is wholly 

 of cartilage, but it supports, in this fish as in Amia, the latei-al 

 edge of the dermo-pterotic. The anterior three-quarters, 

 approximately, of this cartilaginous portion of the ridge forms 

 the dorsal edge of the articular facet for the hyomandibula, and, 

 as shown in the figures given, it apparently lies along the dorso- 

 latei'al edge of the ridge of the lateral semicircular canal. At 

 the hind end of the facet for the hyomandibula. the ridge is joined 

 by a much less pronounced one, which forms the ventral edge of 

 the facet for the hyomandibula, the two ridges, united, then con- 

 tinuing onward a short distance as a stout and rounded ridge, 

 which lies along the lateral, instead of the dorso-lateral, surface 

 of the i-idge of the lateral semicircular canal and ends somewhat 

 abruptly with a curved hind edge slightl}'' posterior to the 

 anterioi- edge of the epiotic bone and some little distance anterior 

 to the transverse plane of the vagus foramen. The marked, 

 postero-laterally projecting corner at the hind end of this ridge 

 of Amia (Allis, '97, fig. 8) is thus wanting in Lepidosteus, but 

 the ridges of these two fishes must, nevertheless, have approxi- 

 mately the same posterior extent, for the hind end of the ridge 

 is traversed in each of them by a canal which transmits the 

 I'amus dorsalis of the nervus glossopharjaigeus. 



Along the lateral portion of the doi'sal surface of the chondro- 

 ■ cranium there is a sulcus longitudinalis, which is bounded 

 laterally by the spheno-pterotic ridge and mesially by a ledge, 

 the rounded edge of which lies at a much higher level than the 



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