442 



have given above, is based, partly on the observations of Vogt, Eathke, and 

 Itemak, and partly on my own. As great misunderstanding seems to me 

 to have prevailed on this head, I have put together in the present note, 

 all the most important evidence I have been able to collect on this highly 

 interesting subject, accompanying it with a running commentary. I have 

 done this the more willingly, as the accounts of the mode of development 

 of vertebrae in general, in our own language, which I have met with, are 

 strangely meagre. 



Development of the Spinal Column in Fishes. 



1. Blennius viripams (Rathke, 'Bildungs- und Entwickelungsgeschichte 

 des Blennius viviparus.' 1833). 



The surface of the notochord hardens, and acquires a fibro-membranous 

 consistence, while its inner substance becomes glassy and transparent, so 

 that the notochord is separated into sheath and contents, as in the lamprey. 

 A segmentation next takes place in the sheath. " At successive inter- 

 vals it increases, more and more, in density and solidity, acquires in places 

 almost the constitution of cartilage, and there thus arise a great number 

 of successive, very fine, narrow rings, which are connected by much nar- 

 rower, far less solid, but also far less transparent and more whitish-coloured 

 parts, like sutures." 



When this segmentation has commenced, " a number of cartilaginous, 

 very short, thin and rod-like processes, which run in pairs from each 

 member of the vertebral column, where its upper side passes into the two 

 outer ones, appear, pass upwards in the walls surrounding the spinal mar- 

 row, and enclose its lower cords. At first, therefore, each pair of processes 

 are separated by a considerable interval throughout their entire length. 

 Subsequently their upper ends approximate (increasing in length, and at 

 the same time accommodating themselves to the curve of the spinal 

 marrow, and bending round it) more and more closely, till they, at last, 

 meet above the spinal marrow, and soon after this has happened, coalesce 

 into an arch. 



" Contemporaneously with these processes, and in the same way, there 

 arise from the vertebral column (though only from its hinder half, or that 

 which constitutes the foundation of the tail) a number of other processes 

 similar in form and structure, which spring from the junction of the under 

 with the lateral faces of the column. These take the opposite direction 

 to the preceding, tend to enclose the great caudal vessels, and unite in 

 pairs into arches, which lie in a series and correspond with the vertebral 

 segments." 



From the segments of that part of the vertebral column which lies 

 between the tail and the head, there grow out, in corresponding places to 

 those in which the crura of the inferior arches take their origin from the 

 vertebral segments of the tail, and in the same manner and at the same 

 time, many cartilaginous processes, which attain, however, only a very 

 slight length, and also take a transverse direction. They might be regarded 

 as lateral pieces of the transverse processes of the higher animals ; but it 

 is more probable that they correspond with the ribs of other Vertebrata. 



