42 MR. E. P. ALLIS O:^ POSTORUITAL ARTICULATION OF 



musculus levator arcus palatini (Allis, 1897). It lies between 

 the musculi levator arcus palatini and adductor mandibulse, 

 giving insertion, on its internal surface, to certain fibres of the 

 former muscle and origin, on its external surface, to certain 

 fibres of the adductor. It forms the lateral boundary of the 

 surface of insertion of the levator on tlie palatoquadrate, the 

 mesial boundary of that surface being formed by the processus 

 basalis together with that portion of the dorso-mesial edge of the 

 metapterygoid that lies between tliat process and the processus 

 metapterygoideus. That branch of the nervus trigeminus that 

 innervates the levator arcus palatini turns posteriorly around the 

 anterior edge of that muscle, and runs posteriorly on its external 

 surface, thus lying, morphologically^, between the processus 

 basalis and the processus metapterygoideus, dorsal to the one and 

 ventro-mesial to the other. That branch of the external carotid 

 that becomes the secondary afferent pseudobranchial artery 

 (Allis, 1912) has similar relations to these two processes, as has 

 also the vena jugidaris. The efferent pseudobranchial artery 

 runs upward and forward ventro-mesial to the processus meta- 

 pterygoideus, but its relations to the processus basalis are not 

 positively evident. It lies external to the ascending process of 

 the parasphenoid, and hence would seem to lie morphologically 

 ventral to the processus basipterygoideus. 



In embryos of this fish up to 19-5 mm. in length, the two pro- 

 cesses here under consideration are shown by Pehrson (1922, 

 figs. 3-12) appai^ently botli lying on the dorso-mesial edge of the 

 palatoquadrate, the metapterygoid process lying posterior to the 

 basal process and extending farther dorsally in all stages 

 excepting the very earliest. In a 56 mm. specimen, the meta- 

 pterygoid process has apparently begun to assume its adult 

 position, and the metapterygoid bone has begun to ossify, and it 

 is to be noted that Pehrson shows (/. c. fig, 14) the unossified 

 portion of the pterygoquadrate cartilage forming a Y-shaped 

 mass, the basalis and metapterygoideus processes forming the two 

 arms of the V, and the metapterygoid bone lying betw^een them, 

 in the hollow of the Y, and not extending upward into either 

 process. The otic process of this fish, and that of the Teleostei 

 as well, is represented in the lateral wall of the trigemino-facialis 

 chamber (Allis, 1914). 



The characteristic features of these two processes of this fish 

 thus are: that one of them lies postero-lateral to the other; that 

 the antero-mesial one is directed towai^d the lateral edge of the 

 floor of the cranium, where the palatoquadrate articulates with it 

 in Lepidostei(.s ; that the postero-lateral one is directed toward 

 the lateral edge of the roof of the cranium, where the palato- 

 quadrate articulates with it in Hexanchus and Heptancliiis ; that 

 the musculus levator arcus palatini has its insertion on the 

 palatoquadrate between the two processes; that the musculus 

 adductor mandibulse lies external to the processus metaptery- 

 goideus and is cut ofF, by it, from any origin or insertion on the 



