PALATOQUADRATE WITH NEUROCRANIUM IN CCELACANTHIDS. 57 



the neurocranium dorsal to the vena jugularis, is either traversed 

 by the truncus hyomandibularis facialis or lies anterior to that 

 nerve (Polypterus), and is, if I am correct in my conclusions 

 (AUis, 1918), developed from the branchial rays of the hyal arch, 

 while, in the Plao,iostomi, the hyomandibula articulates with the 

 neurocranium ventral to the vena jugularis, and is developed 

 either from the pharyngeal or the epal element of the hyal arch 

 (Allis, 1915). In Polyodon, where the hyomandibula articulates 

 with the neurocranium dorsal to the vena jugularis, and is of the 

 teleostome type, it nevertheless differs from that in the bony 

 fishes in that it lies posterior to the nervus facialis, and in this 

 fish the hyomandibular canal has a position intermediate between 

 the two above referred to. There may be no morphological 

 significance in this, for there is in certain of the Plagiostomi a 

 line of surface pit-organs that has a position similar to that of the 

 preopercular canal of the bony fishes, and in certain of the latter 

 fishes there are surface lines of pit-organs that correspond in 

 position to that of the hyomandibular canal of the Plagiostomi ; 

 but it is to be noted that in the Coelacanthidae, where a hyoman- 

 dibula, although presumably present, has not yet been found, the 

 hyomandibular canal has the position of that in the Plagiostomi, 

 while in the Palaeoniscidfe, where the hyomandibula was well 

 developed and of the teleostome type, the canal has the position 

 of that in the bony fishes. In the Stegocephali, the canal on the 

 cheek would seem to be formed by the horizontal portion of 

 the canal of the Plagiostomi together with the dorsal portion 

 of the preopercular canal of the bony fishes. 



Literature cited. 



Allis, E. P., Jr. 1897. The Cranial Muscles and Cranial and First Spinal 



Nerves in Amia calva. Journ. Morph. vol. xii. 

 „ J, ^ 1903. The Skull, and the Cranial and First Spinal Muscles 



and Nerves in Scomber scomher. Journ. Morph. vol. xviii. 

 „ „ ^ 1909. The Cranial Anatomy of the Mail-cheeked Fishes. 



Stutt. Zoologica, Bd. xxii. 

 „ „ — 1912. The Pseudobranchial and Carotid Arteries in JEsox, 



Salmo, and G-adus, together with a Description of the 



Arteries in the Adult Amia. Anat. Anz. Bd. xli. 

 „ ,, "-^ 1913. Certain Homologies of the Palatoquadrate of Sela- 



chians. Anat. Anz. Bd. xli. 

 ;, „ "^ 1914. The Pituitary Fossa and Trigemino-facialis Chamber 



in Ceratodus fosteri. Anat. Anz. Bd. xlvi. 

 „ „ V 1915. The Homologies of the Hyomandibula of the Guatho- 



stome Fishes. Journ. Morph. vol. xxvi. 

 „ „ -J 1918. On the Origin of the Hyomandibula of the Teleo- 



stomi. Anat. Rec. vol. xv. 

 „ ,, 1922. The Myodome and the Trigemino-facialis Chamber 



in the Ccelacanthidse, Rhizodontida;, and Palseoniscida;. 



Journ. Anat. vol. Ivi. 

 Bridge, T. W. 1895. On Certain Features in the Sknll of Osteoglossum 



formosum. Proc. Zool. Soc. London. 

 Beoom, R. 1922. On the Persistence of the Mesopterygoid in certain 



Reptilian Skulls. Proc. Zool. Soc. London. 

 Betant, W. L. 1919. On the Structure of JEusthenopteron. Bull. Bufialo 



Soc. Nat Sci. vol. xiii. 



