196 AYERS AND JACKSON. [Vol. XVII. 



on each side, a short, thick lateral process which connects the 

 trabecula with the palatine bar {PI). The space enclosed by 

 the trabeculae (including the hypophysial plate) and the an- 

 terior halves of the parachordals we shall call the hypophysial 

 fontanelle. The floor of the membranous cranium occupying 

 this fontanelle forms the roof of the hypophysial canal. This 

 canal is a short tube which opens posteriorly into the pharynx, 

 anteriorly and superiorly into the nasal tube and nasal cap- 

 sule. The floor of the hypophysial canal, which is a part 

 of the roof of the pharynx, is supported by the median 

 unpaired hypophysial plate (PI. XXII, Fig. 6; PI. XXIII, 

 Fig. 7, Hp). It is a flattened cartilaginous plate, very thin 

 posteriorly, but thicker anteriorly. At the posterior end the 

 plate spreads out into two lateral processes, which are some- 

 times bilobed at the tips. These processes, together with the 

 posterior end of the body of the plate, support the posterior 

 margin of the valvular septum between the hypophysial and 

 pharyngeal canals. At the junction of the posterior third with 

 the anterior two-thirds of the hypophysial plate, it widens out 

 laterally on each side to fuse with the corresponding anterior 

 ends of the trabeculae, as previously described. So that the 

 trabeculae, with their hypophysial expansion and the para- 

 chordals, completely encircle the hypophysial canal. Near the 

 anterior end the hypophysial plate divides into two antero- 

 lateral processes (Fig. 7, k) which are closely attached by liga- 

 ments to the inner sides of the palatine bars, a short distance 

 behind their connecting commissure {cm). 



The olfactory capsule as distinct from the entire olfactory 

 chamber (PI. XXII, Figs. 5, 6, oc) is a saccular structure di- 

 rectly in front of, and in size corresponding to, the membra- 

 nous cranium, whereas the whole chamber is tubular in form. 

 Anteriorly and inferiorly the capsule is open, communicating 

 with the nasal tube and hypophysial canal. The posterior 

 wall is formed by the anterior wall of the cranium, and is per- 

 forated near the dorsal margin by a row of foramina on each 

 side which transmit the large branches of the olfactory nerves. 

 The lateral and dorsal walls of the olfactory capsules are sup- 

 ported by a framework of cartilage which may be described as 



