THE CHONDROCRANIUM IN THE ICHTHYOPSIDA. 125 



otic capsules leaving no suggestion of their former sepa- 

 ration, except in the jugular foramina (Fig. 29 j). The 

 notochord extends forward beyond the middle of the otic 

 region. Its sides are embraced by the two halves of the 

 basilar plate. At its apex it projects freely forward for 

 a short distance. Except for a small fontanelle (/} , the bas- 

 ilar plate is continuous with the walls of the otic capsules 

 which are united above by a broad, arched synotic tec- 

 tum. The positions of the semicircular canals are clearly 

 indicated in the external surface of the otic capsules. No 

 median wall separates the cavity of the ear from that of 

 the brain. In front and a little below the jugular fora- 

 men there is another smaller foramen through which the 

 ninth nerve {ix) passes out of the cranium. Farther for- 

 ward there are three more apertures in the ventral wall of 

 the capsule. The posterior of these is the fontanelle men- 

 tioned above. The middle one of the three is small and 

 is traversed by the hyomandibular branch of the facial 

 nerve {hy) . The anterior foramen is for the exit of a 

 branch of the jugular vein (jv). 



The basilar plate is continued forward into a trabecula 

 upon either side. These extend separately to a point in 

 front of the hypophysis and then unite along the median 

 line in a narrow tral)ecular band. This baud has the shape 

 of an inverted trough and reaches to the anterior end of 

 the skull, expanding in the nasal region into the ethmoid 

 plate which forms the floor of the nasal capsules. The 

 palatine branch of the seventh nerve (Fig. 28,paZ) passes 

 downward through a foramen in the posterior end of the 

 trabecula. Two slender supraorbital bands {sh) arise 

 from the anterior ends of the otic capsules and curve 

 forward and inward, until about half way from the otic to 

 the nasal region, where they enter the margins of the 

 arched tegmen cranii which covers the anterior end of the 



