34 ILLINOIS BIOLOGICAL MONOGRAPHS [34 



The foramen for the passage of the ophthalmicus superficialis trigemini 

 (Fig. 4, oph. v.), which earlier was entirely in cartilage, has now ossified on its 

 ventral external side, so that the nerve is enclosed in an osseous canal posterior 

 to and above the optic foramen. The ophthalmicus superficialis facialis 

 (Fig. 4) issues through a foramen in the cartilage just above the opening of 

 the osseous canal of the opthalmicus superficiaUs trigemini and innervates 

 the lateral line canal organs of the anterior part of the supraorbital canal which 

 lie in the frontal and nasal bones (Fig. 11). 



The roof of the cranium posterior to the internasal septum is formed by 

 the frontal ossifications (Fig. 3) and the very thin cartilaginous epiphysial bar. 

 The latter is now relatively much farther posterior to the ethmoid region than 

 it was previously and lies in about the same transverse plane as the optic fora- 

 mina. Dorsally it is covered by the broad frontals, which are separated from 

 each other in the mid-dorsal line by a very narrow fontanelle except in the region 

 immediately above the epiphysial bar where they interdigitate. These frontal 

 ossifications are the largest in the roof of the cranium at this stage; they project 

 laterally above the orbit in continuation with the derm-oectethmoid (Fig. 4). 

 The ventral surface of the frontal sits on the dorsal surface of the alisphenoid 

 and tegmen cranii cartilages (Figs. 32, 39) and extends down the outside face of 

 the former without being at all intimately connected with the perichondrium of 

 the cartilage. Behind the eye each frontal is grooved for the reception of the 

 suborbital lateral line canal and articulates with the posterior ossicle of the 

 infraorbital series (Fig. 3). The suborbital canal enters the frontal at this 

 point and unites with the posterior end of the supraorbital canal to form a canal 

 which extends posteriorly on to the dorsal surface of the (Fig. 11) sphenotic ; this 

 condition persists in the adult. The ossification surrounding the supraorbital 

 canal (Fig. 32.) is indistinguishably fused with the membranous frontal ossifica- 

 tion. This canal runs anteriorly within the frontal to a point just posterior to 

 the union of the supraethmoid and frontal, and from here passes into the con- 

 nective tissue surrounding the posterior end of the nasal bone and thence into 

 the latter (Fig. 11.). From the junction of the supraorbital and suborbital 

 canals, a tubule, enclosed in an osseous canal, runs obliquely posterior toward 

 the middle line of the frontal and opens through a small pore on its dorsal sur- 

 face (Fig. 3, /. p.). Another dermal tubule leaves the frontal through a pore in 

 its dorsal surface just posterior to the entrance of the supraorbital canal into 

 the frontal from the nasal (Fig. 3, /. p.) 



The infraorbitalia (Fig. 3) are a series of slender, cylindrical, pipe-like bones, 

 beneath and behind the eye, including within them the suborbital lateral line 

 canal. They are six in number, each separated from its successor by the pas- 

 sage of a tubule from the enclosed canal to the external surface of the head, a 

 so-called dermal tubule (Fig. 11.) The most anterior bone of this series con- 

 nects with the ventro-lateral margin of the lacrimal bone into which the sub- 

 orbital lateral line canal passes. These bones are typical of the teleosts. 



