ORAL CIRRI OF SILUROIDS AND ORIGIN OP THE HEAD IN VERTEBRATES. 1 1 



A small pterygoid cartilage (Pty. Fig. 9) is independently formed 

 much farther forward. It may be seen on the left of the figure partly 

 hidden by the prepalatine piece. The cartilaginous apophyses of the 

 prepalatine piece (Prepal.) remain as a small portion at the articu- 

 lation near the base of the rostrum and a large distal block. 



Above the prepalatine cartilage is the nasal tentacle with a slight 

 basal expansion. This forms the outer wall of the anterior narial 

 opening. 



The rostrum bears at its tip the upper tentacle-like support of 

 the velum (m.v.s). A small nodule of precartilage is seen on the left 

 between the prepalatine and the velar supports. The maxillary 

 tentacle (Mx. t.) does not rest on the prepalatine piece but is supported 

 by the intermediation of the maxillary bone. Its base is bifurcated 

 on the left side of the figure. 



The Meckelian cartilage (Mck.) is represented as a triangular block. 

 The posterior portion has undergone partial resorption and the posterior 

 angle is far from reaching the quadrate. The upper angle is prolonged 

 into a vertical somewhat anteriorly directed coronoid process (Proc. cor.) 

 to which is affixed the procartilagicous coronoid piece (Cor. p.) which 

 is large and passes continuously into the coronoid tentacle. The tentacle 

 (Cor. t.) turns downwards, outwards, and backwards. The anterior 

 angle of the Meckelian cartilage is produced into the mentomeckelian 

 process (m. Mck.) which is short and very far from reaching its fellow 

 of the opposite side. The distance of the mentomeckelian processes 

 from each other is well shown in the figure. 



A stylohyal cartilage (Sty. hy.) is present and bears the ceratohyal 

 which is very thick at its two ends. In the specimen the middle 

 portion was replaced by perichondrial bone on one side. The distal 

 extremity bears a hypohyal. 



The postero-ventral tip of the ceratohyal bears a procartilaginous 

 prolongation (* Fig. 9) which supports the uppermost branchiostegal 

 ray. It may perhaps be considered the homologue of one of the car- 

 tilaginous branchiostegal rays of Selachii. 



Model ofCallichthys (Figs. 6, 7, 10). 

 Specimen 3 cm. in length. Sections 25 jj. thick. Fvery second 

 section drawn, with magnification 28. (Zeiss, Oc. 2, Ohj. aa). Height of 

 drawing above table 19 cm. Wax plates 1-2 mm. thick. 



