692 DR. P. CHALMERS MITCHELL ON THE 



Unfoitnufitely, owing to the very complete union of the bones 

 concerned, these cannot be interpreted completely without the 

 examination of very young skulls, but comparison of adult skulls 

 shows a good deal worth noting. In Balcenice2:>s the size of the 

 brain is small in proportion to the size of the bird, with the 

 result that the skull is very short between the orbit and the 

 posterior end. Attachment for the powerful temporal muscle is 

 increased by the strength and size of the postfrontal process 

 (PI. LXXXI. fig. 1), which depends as a triangle of bone behind 

 the orbit, with the external face strongly ridged. The blunted 

 apex of the ti'iangle reaches nearly half-way down to the qnadrato- 

 jugal bar and is continued to a strong tubeicle on the latter by a 

 fibrous band. The central portion of the band has a separate 

 ossification, and it would not be surprising to find, in an old bird, 

 that calcification of the fibrous band had joined this central ossi- 

 fication with the postfrontal above and the jugal below, to form 

 a complete beam of bone separating the orbital and temporal 

 cavities externally. Owing to the complete fusion of the bones, 

 it is impossible to be certain as to the exact composition of the 

 postfrontal. A more primitive skull like that of Drovuetts (in 

 which the propoition of the temporal region to the rest of the 

 skull closely resembles that in Bakmice^js) shows that the ali- 

 sphenoid contributes the main portion of the postfrontal, and 

 that the frontal grows down over it only about half- \^ ay. In 

 Balcenicejis it appears as if the frontal covered the alisphenoid 

 right down to the lower end of the postfrontal, and on the 

 postei'ior face the alisphenoid may itself be covered by a process 

 of the squamosal. On the other side of the temporal cavity in 

 many birds the squamosal sends forwards and downwards from 

 just over the quadrate articulation a stout beam of bone pio- 

 jecting towaids the point of the postfrontal. In Balaniceps this 

 is repi'esented only by a nari^ow edge projecting over the quadrate 

 articulation. Scopus (PI. LXXXI. fig. 2) has like Balceyiicejjs also 

 a. small brain and narrow temporal space. The postfrontal has 

 almost exactly the relations of that of Balceoiiceps, but it does not 

 reach neaily so far towards the jugal. The spur of the squamosal 

 is minute, and allowing for differences in the strength of the 

 muscular attachments, this region is almost the same in Scopus 

 and BalcenicejJS. 



In a large Stork like Xenorhynclms (PI. LXXXI. fig. 3) there 

 is an arrangement strikingly dift'erent in appearance but which, 

 none the less, can be interpreted easily. The brain is still small 

 and the temporal cavity narrow. The postfrontal triangle narrows 

 very rapidly and is continued downwards as a slender bar which 

 stops short long before the jugal is reached. Clcse scrutiny seems 

 to show that the frontal contributes a superficial splint-like 

 factor, running down almost to the tip on the anterior face, and 

 that the squamosal forms the greater portion of the lower and 

 posterior part, but how much the alisphenoid contributes it is 

 impossilile to say. Tho spin- of the squamcsal from over the 



