120 MORPHOLOGICAL TYPES 



neossoptiles. Filoplumes, plumutee, and pennse are preceded 

 by preflloplumes, preplumulae, and prepennae, respectively. 



Feathers are usually coloured, and since they are dead 

 structures, their colours are due either to pigment which they 

 contain, or to the optical properties of their texture. Feathers 

 are moulted and replaced periodically, which in many birds 

 enables plumages of different type and colour to succeed one 

 another. Flight-feathers are usually moulted in pairs, sym- 

 metrically right and left, as a result of which the bird is still 

 able to fly during the moulting period. 



Skull. — The skull of the pigeon, as of birds generally, is 

 strongly ossified, so much so that the bones tend to fuse 

 together and the sutures between them to disappear. The 

 brain-case is much enlarged compared with lower animals. 

 Covering the roof are : nasals, prefrontals, frontals, parietals, 

 and squamosals (membrane-bones). The cartilage-bones of 

 the neurocranium are : basioccipital, supraoccipital, ex- 

 occipitals, basisphenoid, laterosphenoids, orbitosphenoids, and 

 ethmoid. The brain-case does not extend forward between 

 the eyes, which are only separated by an interorbital septum. 

 The bones of the auditory capsule fuse and form the periotic. 



The parasphenoid of lower forms is represented by the 

 median rostral, and the paired basitemporals, which latter are 

 attached to the underside of the basisphenoid. There is a 

 single occipital condyle. 



It is worth noticing that the squamosal now forms part of 

 the wall of the brain-case ; the latter is so much enlarged that 

 the cartilage-bones are insufficient to enclose it (see Fig. 140). 



The quadrate articulates with the periotic by an otic process. 

 Stretching forwards from the quadrates are two strings of 

 bones on each side. On the outer side are the quadrato-jugal, 

 jugal, maxilla, and fused premaxillae, all membrane-bones 

 forming the margin of the upper jaw. Median to these, the 

 pterygoids run forwards from the quadrates, and articulate 

 with the basipterygoid processes of the basisphenoid, and with 

 the palatines, which run forwards to the maxillas. Median to 

 them are the small prevomers, fused together in the middle 

 line. 



