THE-CHONDROCKANIUM OF LEPIUOSTEUS. 259 



and strongly defined ridge, the anterior portion of which lies on 

 the chondrocranium and the posterior portion along the lateral 

 edge of the dermal parieto-pterotic. When this latter bone is 

 removed, that part of the ridge that lies on the chondrocranium 

 is seen to vanish posteriorly along the dorsal surface of the 

 opisthotic process, the ptei"otic and ojaisthotic lidges of the 

 chondrocranium thus being there confluent. The sphenotic 

 portion of the spheno-pterotic ridge is not well defined in the 

 region of the postorbital process, but, anterior to that process, an 

 anterior continuation of it is formed by the lateral edge of that 

 long, anteriorly projecting, process-like portion of the postfronto- 

 sphenotic that is shown in Traquair's ('71) figures of this fish. 

 Between this process-like portion of the postfi'onto-sphenotic and 

 the sphenoid bone, there is a large supraorbital fontanelle, roofed 

 by the frontal, and the niusculus temporalis has its origin on the 

 ventral surface of this roofing portion of the frontal bone. The 

 postorbital bone is attached both to the anterior end of the 

 process-like portion of the postfronto-sphenotic and to an ad- 

 jacent angle on the lateral edge of the frontal, the posterior 

 margin of the (.)rbit tlius lying considerably anterior to the 

 postorbital process of the chondrocranium. 



The conditions in a few of the higher vertebrates may now be 

 considered, the supraotic depression, which is found more or less 

 developed in all of them, being left out of further consideration. 



In a 29 mm. embryo of Rana fusca, Gaupp ('93) describes a 

 so-called processus oticus quadrati which is said to be a short rod 

 of cartilage which extends from the most postero-lateral portion 

 of the quadrate to the most antero-laterally projecting portion of 

 the i-idge of the lateral semicircular canal. It is said to be, as its 

 name imj3lies, a process of the quadrate, but it has exactly the 

 position of that posterior part of the sphenotic portion of the 

 spheno-pterotic ridge of Veit's 201 mm. embryo of LepidosUus 

 that lies lateral to the recessus dorsalis spiracularis. In an older 

 specimen of Nana, at a stage which represents the end of the 

 period of metamorphosis, a strong and overhanging ridge has 

 developed along the outer surface of the ridge of the lateral 

 semicircular canal, at the point where the processus oticus 

 quadrati had previously fused with the latter ridge. Gaupp calls 

 this overhanging ridge the crista parotica, and the so-called 

 processus oticus quadrati forms a connection between the outer 

 edge of this crista and the postero-lateral corner of the quadrate. 

 In a still older specimen, a young frog immediately after the 

 metamorphosis, the crista parotica is said to be much more 

 strongly developed, and to form a sort of roof to the tympanic 

 cavity (Paukenhohle) ; and, because of this, Parker is said to 

 have called this ridge the tegmen tympani. The processus 

 oticus quadrati is said to have now been absorbed by the crista 

 parotica, and it is the body itself of the quadrate that rests 

 against, and is fused with, the so-formed crista joarotica. The 

 vena jugularis lies directly beneath this crista, and the nervus 



Proc. ZooL. Soo.— 1919, No. XIX. 19 



