79] THE SKULL OF AM lURUS— KINDRED 79 



chondrial ossification and hence this part of the sphenotic is not comparable to 

 the true postfrontal. He does not attempt to explain to what bone this dermal 

 derivative may be compared. In Amiurus, as in many other teleosts, the 

 perichondria! ossification on the chondrocranium is fused with a dorsally lying 

 lateral canal ossification (Figs. 19, 32>). McMurrich also noticed this in his 

 work on Amiurus. If the postfrontal of Amiurus is to be regarded as the 

 superior infraorbital bone, then this lateral line canal ossification, above the 

 sphenotic, must be an element which has no homologue in the higher groups 

 and is developed for the protection of the canal alone, eventually sinking in and 

 becoming intimately connected with the perichondrial ossification. That it 

 takes only a minor part in the formation of the broad roof of the bone can be 

 seen by the way in which the major part of the bone is developed medial to it 

 on the surface of the otic capsule. 



The homologies of the remaining parts of the bone in the Teleostomes are 

 easy to trace. The lateral face is usually grooved for articulation with the 

 hyomandibula and is related in Amiurus to the anterior and posteriorly situated 

 bones. In most Teleostomes the sphenotic does not have the ventral extent 

 found in Amiurus, nor does it occupy as much of the dorsal surface of the 

 cranium. In Scomber (Alhs, 1903) and the Loricati (AUis, 1910), the relations 

 of the ramus oticus facialis are comparable to the condition in Amiurus. 



There is a great deal of cartilage within the bone and sometimes, as in 

 Salmo, there is no internal ossification. The relation of the bone to the recess 

 for the anterior semicircular canal is a constant feature, although in most fishes 

 the canal extends only part way into it. 



In some of the Cyprinidae the lateral part of the dorsal surface of the bone 

 is grooved for the insertion of the dilitator operculi hgament and muscles as 

 in Amiurus. In other teleosts this fossa lies more upon the posterior margin 

 of the frontal than upon the sphenotic. It may be said however, that the 

 sphenotic usually forms a part of the dilitator fossa. 



The prootics. These bones form the floor and most of the lateral walls of 

 the cavimi cranii, posterior to the suprasphenoid and the foramina for the 

 passage of the seventh nerves. As noted above (Figs. 4, 26), they develop 

 around the anterior parachordals and the ventral part of the otic capsules. 

 They are fused with each other in the median line of the cranial floor, below and 

 posterior to the hypophysis. A large amount of the original cartilage remains 

 in both the lateral and ventral parts of the bone, for the most part encased in a 

 perichondrial osseous lamella and continuous with the cartilage of the surround- 

 ing bones (Fig. 7). That part of the bone which forms the posterior margin of 

 the trigemino-facial foramen is exceedingly thin and transparent. In tracing 

 the development it was noted that the cartilage which originally formed the 

 posterior margin of the foramen in the 10 nmi. stage did not keep pace with 

 the growth of the cartilage of the surrounding parts, so that in the 32 mm. stage, 



