480 



Prof. W. K. Parker. 



[Mar. 22, 



of the evolution of ribs. Towards the end of that chain, the vertebras 

 and ribs form the upper part of the most highly specialised thoracic 

 cage in existence, it is the last consummation of the whole evolutional 

 series, the furthest from the beginning made by the Ammocoete, when 

 it has just been metamorphosed into a Lamprey. 



In the Cormorant, one of the lower forms of the Pelecanine 

 Family (" Steganopods," " Dysporomorphas "), the vertebral chain is 

 much more archaic than in either the Swan, or even the Ostrich and 

 its kindred. 



Here, indeed, we miss the atlantal rib, but rudiments are present 

 on the axis, and these are attached to an ankylosed intercentrum. 



On the whole, the greater number of the styloid cervical ribs are 

 like those of the Swan, except that the upper edge of the free style is 

 not connected with the neural arch by an ossified aponeurosis. There 

 are only three presacral vertebras that have developed ribs 

 attached to sternal pieces, and thus forming perfect cinctures, finished 

 below by the common inverted keystone or sternum. The ribs on the 

 last two cervicals, the nineteenth and twentieth, have perfect heads, 

 and have uncinate pieces attached and ankylosed to them, but their 

 sternals are suppressed. In front of them there are three vertebras, 

 with non-segmented riblets, that have no retral style ; these are mere 

 necks of a developed rib, and run almost horizontally from the centrum 

 to the large diapophysis ; they are, in fact, similar to, but much 

 stronger than, the atlantal rib of the Swan. The parapophysis in these 

 three vertebras stretches straight out from the centrum, which is also 

 alate behind it, and these bars enclose a large foramen, 8 mm. wide and 

 4 mm. high. The nineteenth cervical, with its developed vertebral 

 rib, forms for the capitulum of that rib a deep cup with two 

 distinct facets, so that the head of the rib articulates in a manner 

 similar to what is seen in Mammals. In them, however, the two facets 

 are one in front of the other, and on distinct vertebras ; here they are 

 one above the other, and near the f ore-end of the same vertebra, one 

 is on the centrum, and the other is on the neural arch. The facet on the 

 centrum is higher than the junction of capitulum an! centrum, in the 

 non-segmented rib next in front. In the last cervical, the lower facet 

 is still higher, but is on the centrum ; both these pairs of ribs have a 

 long neck and the normal articulation of the tuberculum with the 

 under face of the end of the large diapophysis, an outgrowth of the 

 neural arch. 



In the three dorsals the parapophysial cup for the capitulum is 

 entirely on the neural arch, and, from before, backwards, it keeps rising 

 to a higher point in that arch. Thus in a few vertebras we have the 

 capitulum rising from a point where the intercentrum would he if it 

 were developed, to a point quite clear of, and some height above, the 

 centrum itself. The first general sacral vertebra is similar to the last 



