44 MR. E. P. ALLIS ON POSTORBITAL ARTICULATION OP 



the hind edge of the metapteiygoid, is no more extraordinary 

 than the incorporation, in this fish, of the dorsal portion of 

 the preoperciilum in the hind edge of the hyomandibula ( Kindred, 

 1919). Tiie metapterygoid, the projecting dorso-mesial portion 

 of wliich forms tiie processus basalis, is said to he attached to 

 the lateral surface of the cranium by a sheet of muscular and 

 ligamentous tissue. It is not said at what point on the lateral 

 wall of the cranium this sheet of tissue has its attachment,, but 

 two sectional views given through the postorbital region would 

 seem to show that the attachment is either to the trabecula or 

 to the lateral edge of the parasphenoid. 



In all of the above-mentioned fishes the palatoquadrate has no 

 direct articular contact with the neurocranium, this articulation 

 being acquired through the intermediation of the hyomandibula, 

 to which the palatoquadrate is firmly fixed. In Lejndosteus, 

 Osteoglossum, Hexanclius, and Hej^tanclids this articulation with 

 the cranium through the intermediation of a hyomandibula still 

 occurs, biit in each of them there is, in addition, direct articular 

 contact with the postorbital portion of the cranium ; and these 

 are the only recent fishes I hnow of in which the latter articu- 

 lation is found, for the palatobasal articulation, found in many 

 of the Selachii, is orbital in position and not postorbital. Gaupp 

 says (1905, p. 767) that an articulation of the palatoquadrate 

 with a processus basi]Dterygoideus is found in many fishes, but, as 

 he does not mention the particular ones, I liave not been able to 

 control the statement. Luther (1913) describes the articulation 

 in Lejnclosteus, and then says that it is also found in Osieoglossuin 

 but in no other teleost. It apparently occurs in certain fossil 

 fishes, as in Boreosomus, one of the Palaeoniscidfe described by 

 Stensio (1921). 



In the adult Lejndosteus, Parker (1882) describes two processes 

 related to the metapterygoid, one of which he calls the pedicle 

 and the other the otic process. The pedicle is the larger of the 

 two, and is shown forming the dorso-postero-mesial corner of the 

 metapterygoid, the so-called otic process projecting ventro- 

 posteriorly f rom the ventral edge of the base of the pedicle. The 

 hind end of the pedicle articulates with the anterior edge of a 

 processus ba,sipterygoideus which projects antero-laterally from 

 the lateral wall of the cranium near its ventral edge, the so-called 

 otic process projecting posterioi-ly ventral to the processus 

 basipterygoideus. In a 20^ mm. embryo of this fish, these two 

 processes of the metapterygoid form (Veit, 191), fig. 17, pi. 0.) 

 the dorsal and ventral corners of the actual hind edge of the 

 palatoquadrate, but as this edge of the palatoquadrate of this fish 

 corresponds to the metapterygoid portion of the dorso-mesial 

 edge of the palatoquadrate of Amia, the two processes lie, 

 morphologically, one posterior to the other on the posterior 

 portion of the dor-so-mesial edge of the palatoquadrate. They 

 accordingly agree exactly, in this, with the basalis and metaptery- 

 goideus processes of Amia, and I shall hereafter so refer to them. 



