51] THE SKULL OP AM lURUS— KINDRED 51 



bone. The morphology of this bone will be discussed under the adult descrip- 

 tion. Sagemehl (1891) claims that the supraoccipital of the adult is a new 

 formation in the teleosts and is not found in the ganoids nor in the dipnoi, and 

 that it is the result of a fusion of one or more vertebra with the protometameric 

 cranium. 



In Salmo (Schleip), paired parietalia are present and form discrete bones 

 in the adult. In the larva they develop as dermal sheets dorsal to the otic 

 capsules, fused anteriorly to the frontals, laterally to the squamosal element 

 of the squamoso-pterotic, and medially to the anterior ends of the supraoccipi- 

 tal. They are separated from the cartilage of the otic capsule by fibrous con- 

 nective tissue. 



In Amiurus there are a pair of such dermal ossifications in the same region 

 and having the same histological relations. These ossifications are fused 

 medially with the perichondria! ossification on the margin of the posterior 

 fontanelle (Fig. 34). Despite this fusion with the perichondrial ossification, 

 these dermal ossifications are comparable to those of the parietalia in 

 the developing Salmo. The adult cranium shows that these ossifications do 

 not persist as discrete bones as they do in Salmo and other teleosts. Laterally 

 they are connected with the squamosal by a thin stroma of fibrous connective 

 cells (Fig. 3) and anteriorly are continuous with the frontalia (Fig. 3) They 

 have no lateral line relationships. 



The details of the developing supraoccipital ossification have been described 

 by Schleip for the salmon. The main part of this ossification, according to 

 this author, develops as inner and outer lamellae in the perichondrium of the 

 synotic tectum. The median dorsal fibrous septum between the dorso-lateral 

 muscles of the two sides of the body ossifies as a vertical osseous plate above 

 the outer lamella and connected with it. It supports at its dorsal end a hori- 

 zontal osseous sheet developed from the fibrous connective tissue between the 

 muscles and the corium. He calls it the spina occipitis. Both inner and outer 

 osseous lamellae extend forward on the margins of the fontanelle anterior to 

 the synotic tectum and are connected with each other by a transverse fibrous 

 sheet which later ossifies and forms the roof of the cranium in this region. 

 Schleip maintains that this fibrous sheet was originally part of the chondro- 

 cranium whose ontogenetic history has become shortened. 



In Amiurus, at the 32 mm. stage, the synotic tectum, as remarked above, 

 is well developed. Inner and outer osseous lamellae are present in its peri- 

 chondrium (Fig. 34). The ramus lateralis accessorius facialis and the jugular 

 vein of each side are enclosed in a canal formed by this perichondrial ossifica- 

 tion along the posterior margin of the fontanelle. This canal has its anterior 

 end at that point where the nerve and vein extend dorsally from the brain, 

 medial to the anterior end of the posterior semicircular canal. In the 10 mm, 

 larva, this nerve and vein lie dorsal to the cartilage of the roof of the posterior 

 semicircular canal. After that stage was passed the cartilage below the nerve 



