MOEPHOLOGT OF THE GALLINACE.E. 217 



(see " Skull of Marsipobranclis," Phil. Trans. 1883, plate 18) the rudiments of the arches 

 may exist without the vertebral centra; they are the most archaic parts of a carti- 

 laginous vertebra. 



The notochord at this stage is in an ichthyic condition ; it is constricted inside the 

 centra, and is largest at the intercentral or segmental tracts (Plate XXIII. figs. 1-4, n.c). 

 The neural arches project outwards in their fore half; then diapophyses, or transverse 

 processes, are modified at their inner edge, in front, so as to form an oblique articular 

 facet ; behind, the neural arch grows over that facet, forming another which glides upon 

 it ; the latter is the post-zygapophysis, the former the pre-zygapophysis. The ribs, 

 which according to Baur (' American Naturalist,' Oct. 1887, p. 945) are developed 

 from intercentra, and therefore are primarily between the centra, appear in the Chick 

 from the 3rd cervical vertebra, backwards, as small curved styles of cartilage, with their 

 pointed end looking backwards and outwards. These styles at first are about two-thirds 

 the length of the centra, and they lie outside the burrowing vertebral artery. The last 

 two or three of these in the cervical region are actually segmented from the diapophysis 

 and the centrum : the rest are only partially separated from those parts ; they are 

 connected with them by means of newer tissue, a less perfect form of cartilage ; the tissue 

 is continuous, and the riblets, under a lower power, look more distinct than they are 

 actually ; they have, however, their own osseous centre, afterwards. In the 13th, and 

 still better in the 14th, the riblet is segmented off from the diapophysis above, and 

 from the centrum below. The little projection of the latter, to which the primary 

 head (capitulum) is articulated, is called a parapophysis, or lower transverse 

 process ; it is near the fore margin of the centrum. In Mammals the articulation is 

 between the centra, and is, therefore, more primitive, as in them also is the articulation 

 of centrum with centrum. In many things, indeed, the Bird is a much more highly 

 modified type than the Mammal. 



The 15th cervical vertebra has its ribs developed considerably downwards ; they tend to 

 reach the sternum, and are tw r o-thirds the length of the next rib, or the first dorsal. 

 Five pans of these dorsal ribs intervene between the 15th cervical and the first of the 

 general sacral series, the first of which, also, has developed ribs, the sternal pieces 

 of which are imperfect below (Plate XXII., s.r.). All the five dorsal vertebrae 

 have ribs with sternal segments (s.r.) ; both the vertebral and sternal bars go on 

 increasing in length from before backwards. The last cervical and the first dorsal ribs 

 have an " appendage " (u.p.) above their middle, a distinct oval cartilage which looks 

 backwards and upwards. The primary and secondary heads of the dorsal ribs (capi- 

 tulum and tuberculum) are well developed in the dorsal region. In the sacrum 

 (Plate XXIII. fig. 4) the 2nd, 3rd, and 4th vertebrae have riblets like those on the 14th 

 cervical ; one or two pairs of these may remain distinct in the adult. As a rule they 

 become fused with the diapophyses which form strong buttresses to the pre-ilium. 

 On the 9th and 10th of the general sacral series, these riblets reappear ; behind them 

 there is another, right and left ; but the diapophyses and these die out towards the end 

 of the chain, where the imperfect vertebrae ultimately unite to form the uropygial 

 piece. 



