248 MR. E. p. ALLIS ON THE OTIC REGION OF 



along the liiterfil surface of the cranium to join and accompanj'- 

 the vena jugnlaris and the other running outward and ventrally, 

 internal to the opercular bones, into the gill-cover. Posterior tO' 

 the adductor hyoraandibularis, the ridge that forms its sui'face 

 of insertion gradually vanishes along the ventro-la.teral surface of 

 the ridge of the lateral semicircular canal, and, posterior to the 

 ridge, the levatores arcuum branchialium and the adductor and 

 levator operculi have their insertions at a higher level, imme- 

 diately ventral to the hind end of the sjjheno-pterotic ridge, or 

 even posterior to that ridge. In my 80 mm. specimen the 

 hyomandibula is much stouter than in the 20 mm. one, and a 

 definite ridge there forms the ventral edge of its articular facet, 

 this ridge lying a,t about the middle of the depression described 

 in the 20 mm. embryo, and corresponding to the ridge that forms 

 the ventral edge of the facet in Veit's 149 mm. specimen. 



In a 14mm. embryo of Lepidosteus the so-called crista parotica 

 is said by Veit ('11) to be a short ridge which forms the ventral 

 border of the foramen by which the ramus oticus lateralis issues 

 on the dorsal surface of the chondrocranium, and it is shown in 

 the figures given lying anterior to the anterior ex^ge of the 

 articular facet for the hyomandibula, and separated from it by 

 a depressed region which probably lodges the recessus dor!-~alis. 

 spiracularis. The ridge lies between the tiansvei'se planes of the 

 trigeminus and facialis openings of the trigemino-facialis chamber, 

 and, as the lateral wall of that chamber is formed by the otic 

 process of the palato-quadrate (pars ascendens quadra,ti), the 

 crista parotica is a ridge that lies approximately along the line 

 where that process fuses with the cranial wall. The so-called 

 crista parotica of this embryo and the ridge that forms the dorsal 

 edge of the articular facet for the hyomandibula thus have similar 

 relations to structures derived, respectively, from the branchial- 

 ray bars of the mandibular and hyal arches (Allis, '"18). The 

 articular facet for the hyomandibula is said to lie, in this embryo, 

 on the ventral surface of the prominentia ampulhe lateralis, and 

 its dorsal edge is not referred to as a part of the crista parotica.. 

 In 11-12 mm. embryos the hyomandibula is said to be here 

 fused with the wall of the otic capsule. 



The spheno-pterotic ridge of Lepidostei(s, the crista, parotica. of 

 "Veit's descriptions, is thus a ridge which apparently has two 

 distinctljr different parts, which are related, respectively, to the 

 doi'sal ends of the branchial-ray bars of the mandibular and hyal 

 arches. The ridge is of relatively late ontogenetic development,, 

 and there is nothing in the descrijitions of this fish to warrant 

 the assumption that either of its two parts has been developed 

 primarily in special relation to the related branchial-ray bar. 

 Yeit's conclusion ('07, p. 179) that the entire ridge has been 

 developed in I'elation to the articulation of the hyomandibula 

 with this part of the cranial wall is, furthermore, evidently incor- 

 rect, for the hyomandibula of his 149 mm. specimen lies, approxi- 

 mately, beneath the two middle quarters only of the entire ridge.. 



