632 MR. W. G. RIDEW00D ON THE [N OV. 6, 



2. On the Hyoid Arch of Ceratodus. By W, G. Ride wood, 

 B.Sc, F.L.S., Lecturer on Biology at St. Mary's 

 Hospital Medical School. 



[Received October 8, 1894.] 



Since the discovery by Huxley (5) of the hyoinandibular carti- 

 lage of Ceratodus, but little has been published in the way of a 

 detailed description of the hyoid arch, and as the intermediate 

 position occupied by the Dipnoi between the Fishes and Amphibia 

 renders a minute knowledge of every part of their anatomy of the 

 greatest importance, the following short contribution may, by 

 collating the views of various observers, be of some assistance to 

 the student of ichthyopsidan anatomy. 



The most conspicuous element of the hyoid arch is the large 

 ossified ceratohyal (figs. 1 and 2, ch), the extremities of which 

 remain cartilaginous. 



Fig.l. 



Ceratodus font eri. — Hyoid arch, ventral view. (The hyomandibular is 

 not shown.) ch, ceratohyal ; hh, hypohyal ; bh, basihyal. 



Towards its anterior end it is nearly circular in section, but 

 proximally it becomes vertically compressed, with a delicately 

 curved posterior edge ending abruptly against the terminal 

 cartilage. 



The cartilage of the distal or anterior end articulates by a flat 

 surface with the hypohyal. 



