MORPHOLOGY OF TE[,EOSTEAN HEAD 8KELKT0N. 557 



In the light of tliese facts^ considerable interest attaclies 

 to the condition found in Amia, which has been carefully 

 described by Allis. Speaking- of the septo-maxillary (my 

 pre-ethmoid), he says, '^ The ventral surface of the lateral 

 edge of the bone forms the anterior end of a low, longi- 

 tudinal, condylar eminence, which extends backwards along 

 the ventral surface of the lateral edge of the ant-orbital 

 process of the chondrocranium, and gives articulation to the 

 palato-quadrate arch " (98, p. 447). Here, then, is a type of 

 articulation which seems to combine the characters of the 

 disartete and the acrartete conditions, and j-et differs from 

 these in the fact that the attachment of the palatal to the 

 ethmoidal region is neither broken into two, nor confined to 

 the pre-ethmoid. For the description of this type, the term 

 Panartete seems most suitable. From these considerations, 

 and from the developmental facts given above, it is evident 

 that this is a type of articulation which very probably gave 

 rise to the disartete condition, and may possibly have done 

 the same for the acrartete. The settlement of this question 

 rests with a closer study of the Malacopterygii and 

 Lepidosteus : in the former, according to Gegenbaur's 

 descriptions and figures of Alepocephalus, we may expect to 

 find the panartete condition passing into the disartete ; and 

 in the latter, according to Parker, a condition exists which 

 bears the same relations to the a-crartete as does that of the 

 salmon to the disartete, for it possesses a rostrum. It is quite 

 conceivable that all these types of articulation were exhibited 

 also by the immediate Ganoid ancestors of the Teleosts. 



In the lower jaw of the adult stickleback the labial 

 cartilage (/.) is still present. 



The premaxilla alone bounds the gape above. At the pre- 

 vious stage the upper ends of the ascending portions ended 

 in amass of densely nucleated tissue, which lay chiefly on their 

 under side. This mass has now become chondritied (PI. 30, 

 fig. 42, lymx.'), and passes into the bony tissue almost with- 

 out boundary line. This chondrified tissue closely resembles 

 that of the labial cartilage. In the earlier stages of develop- 



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