DEVELOPMENT OF THE SKULL IN THE OSTEICH TEIBE. 125 



so that already their exact limits cannot be seen ; yet it is evident from other 

 members of this group of birds that this temporal belt is partly formed by the basi- 

 sphenoid in the mid line. Not only has the bony matter spread far along the great 

 anterior pterygoid processes, but has also sent out two more (posterior) wings, the 

 ossific matter of which is creeping into the anterior part of the broad investing mass 

 (Plate VIII. fig. 2,p.r.p.). 



The "rostrum" (Plate VIII. figs. 1 & 2, r.b.s.) has greatly increased in size and has 

 become relatively longer, reaching to the extreme limits of the alse nasi and external 

 nasal passages. There is still a thick spheno-occipital synchondrosis, and an oval 

 remnant of the pituitary fontanelle (Plate VIII. fig. 2, p.t.s.). Two oblong jagged 

 centres have appeared in the alisphenoidal cartilage, one above and the other below 

 (Plate VIII. fig. 1, a.s.); they are nearly equal in size, the upper being the longest; 

 there are two nearly equal bones formed in the front in Passer domesticus ; and in 

 Nisus vulgaris there is a small ossicle in front of the main piece. The anterior sphenoid 

 (Plate VIII. fig. 1, o.s.jhs.) is still wholly unossified ; it is, as it were, altogether hindered 

 in its growth and development by the excessive size of the territories bounding it before 

 and behind : lateness of ossification is a very constant concomitant of cramped develop- 

 ment, just as an overshadowed tree is slow in its leafing. 



The ethmoid has commenced to ossify both in its upper and perpendicular portions 

 (Plate VIII. figs. 1 & 3, eth. p.e.) ; but I will defer a description of these until I come 

 to describe a somewhat later stage (Struthio, C). 



The cranial and nasal splint bones (f-p.n.) have increased relatively, as well as really, 

 and the fronto-parietal fontanelle (Plate VIII. fig. 3, fo.) is very small ; the frontals and 

 parietals are coming extensively into contact, and are forming the coronal and sagittal 

 sutures ; the middle third of the lambdoidal suture (Plate VIII. fig. 4) is also complete. 



The nasals and lacrymals (n.l.) are becoming dense through the more perfect ossifica- 

 tion of the fibrous lamina in which they are developed. The same may be said of all 

 the splint bones seen in the facial parts of the skull and in the mandible. The ptery- 

 goid (p.ff.) has become more nearly like that of the adult bird, and the palatine (pa.) has 

 lost the sharp point at its anterior end. The broad proximal, the distal, and metaptery- 

 goid portions of the " os quadratum" (q.) (incus) are still unossified, like the ends of the 

 anterior pterygoid processes ; and the base and shaft of the " columella" (st.) have 

 become bony. But the malleal part of the mandible is stiU soft, even its articular 

 persistent end (Plate VIII. figs. 1 «& 5, ar.). The whole of the lingual cartilages have 

 merely grown, but have not altered theii- condition, as to ossification, from what we saw 

 in Struthio, " A." (Plate VIII. fig. 6). 



Struthio, "C." 

 • In Struthio, C. all these processes have advanced a step or two further, although no 

 new bony centre has appeared. The upper fontanelle has almost disappeared. The 

 superoccipital is spreading laterally, the exoccipitals (Plate VIII. fig. 8, e.o.) have 



