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



sharp ridge forming the dorsal edge of its articular facet. The 

 vena jugularis lies dorsal to this latter ridge, in a groove whicK 

 has a slight ridge along its dorsal edge. Dorsal to this groove, 

 between it and the dorso-lateral edge of the chondrocranium,, 

 the levator maxillte superioi'is and the muscle Csd^ have their in- 

 sertions. The trunk-muscles have invaded the supraotic depres- 

 sion, and occupy the whole of it. The main infraorbital latero- 

 sensory canal lies superficial to the lateral portion of the supraotic 

 depression. 



In the Selachii, there is thus, as in the Holostei and Teleostei,. 

 a spheno-pterotic ridge which is developed wholly independently 

 of the ridge of the lateral semicircular canal, but may lie, in part^ 

 along that ridge. The sphenotic portion of the ridge is developed 

 in relation to the postorbital process, and in Heptanchus gives 

 articulation to the otic process of the quadi^ate. No portion of 

 the ridge has any relations whatever to the articular facet for 

 the hyomandibula. 



In embryos of Polyptems^ Budgett ('02) shows a supraotic^ 

 depression similar to that in Leiyiclosieus, and, as in that fish, it 

 does not become a functional temporal fossa. The lateral edge- 

 of the depression is formed by the pronounced ridge of the 

 lateral semicircular canal, this ridge being called by Budgett the- 

 pterotic ridge. The anterior portion of this ridge is said to give 

 off the " sphenotic wing," which forms a pronounced postorbital 

 process. In a 75 mm. specimen of this fish I find the dorso- 

 lateral edge of the postorbital process forming a pronounced, 

 sphenotic ridge, which vanishes posteriorly along the dorso- 

 lateral edge of the anterior portion of the ridge of the lateral 

 semicircular canal. Posterior to this ridge, another ridge begins- 

 along the same edge of the ridge of the lateral semicircular canal, 

 and there forms the dorsal edge of the articular facet for the 

 hyomandibula, this ridge evidently being developed in definite 

 relation to the facet. Posterior to the facet, this ridge vanishes,, 

 and the dorso-lateral edge of the chondrocranium is there formed, 

 at first by the ridge of the lateral semicircular canal, and then 

 by a ridge which lies at first along the lateral surface of the ridge 

 of that canal, but, farther posteriorly, rises gradually to the level 

 of the dorsal edge of that ridge. Yentral to this ridge, a low 

 and rounded ridge marks the position of the lateral semicircular 

 canal, and the vena jugularis lies immediately ventral to it, 

 between it and the swelling of the bulla acustica. 



In the adult Polypterus there is a strongly developed opisthotic 

 ridge, which begins, anteriorly, at the dorsal edge of the facialis 

 opening of the trigemino-fncialis chamber and runs posteriorly to 

 the summit of the process-like, dorso-postero-lateral corner of the 

 chondrocranium. It forms a projecting roof to the groove that 

 lodges the vena jugularis, and the articular facet for the 

 hyomandibula lies immediately dorsal to it and partly on its. 

 dorsal surface, the ridge thus, in a measure, forming the ventral 

 edge of that facet. The dorsal edge of the latter facet is a sharp^ 



