55] THE SKULL OF AM lURUS— KINDRED 55 



mal and perichondria! ossifications. Allis (1910) has described the bone in this 

 region of the Loricati as the 'supraethmoid'; Sagemehl (1884), a dermal bone in 

 this region of Amia as the 'ethmoid'; Parker (1873) and Gaupp (1906) as the 

 'supraethmoidale,' in Sahno; and Gegenbaur (1878), as the 'ethmoideum 

 medium,' in Alepocephalus. These various terms have been used to a greater 

 or less extent by other investigators, without regard to the significance of the 

 terminology used. I have used the terminology of Parker and Gaupp as it 

 applies better to the bone in Amiurus than any of the other terms. Very few 

 of the authors who describe the morphological relations of the bone have 

 studied its development and earlier histological relations; those who have 

 agree that, in most teleosts, this bone has two parts, dermal and perichondrial, 

 respectively. In the ganoids, as represented by Amia (Sagemehl, 1884), the 

 dermal element alone is present in the same position as that element in the 

 teleosts. A comparison of Amiurus and Amia will be made later, after this 

 bone in the former animal has been discussed. In some of the teleosts, the 

 dorsal surface of this bone is very rugose and is covered with numerous spines. 

 It is usually an unpaired bone, its diverging posterior edges interdigitating 

 with the frontals. 



In Amiurus, the supraethmoid is the terminal bone on the dorsal surface 

 of the cranium (Fig. 10). Its dorsal surface is slightly concave toward the 

 posterior margin where it forms the anterior margin of the anterior fontanelle 

 (fl./.). There are no spines on its dorsal surface, which is covered with fine 

 ridges radiating from the margin of a notch {eth. n.) in the median anterior 

 edge of the bone. Lateral to this notch, which is semicircular in outline, 

 the bone sends out two comua, which form the antero-lateral edges of the bone, 

 and are the result of growth anteriorly of dorsal and ventral dermal ossifica- 

 tions from the ethmoid cornua of the 32 mm. larva, at which stage the ossifi- 

 cations are not present, although they begin to develop in the 60 mm. stage. 

 They fuse with each other anteriorly, forming the sharp anterior margin of the 

 cranium and the anterior wall of the nasal fossa («./.). They enclose a space 

 which extends toward the middle line as far as the perichondrial part of the 

 bone (Fig. 7). The ventral sheet extends posteriorly on the ventral surface 

 of the cranium for a very short distance (Figs. 6, 16). The extent of this 

 ossification can be seen only by removal of the premaxillary bones, which are 

 closely connected to its ventral surface by tough fibrous ligamentous tissue. 

 The anterior margin of the vomer {Vo.) interdigitates with the ventral 

 ossification, and upon removal of it, several spicules from the parasphenoid 

 (Fig. 7 ps.), are also visible in contact with it. 



The parasphenoid lies ventral to a broad surface of cartilage {eth.) which 

 forms the posterior ventral floor of the intemasal septiun. In a longitudmal 

 section through this region (Fig. 7) the relations of the ossifications to the car- 

 tilage are well brought out. The ossification, which in the 32 mm. stage forms 

 a perichondrial layer in contact with the superficial dermal ossification, has 



