5^8 



THE NAT.UEAL niSTOllY EEYIEW. 



into a number of similar segments, subsequently appearing during 

 the process of ossification; whilst in other instances, the segmentation 

 already takes place in the cartilaginous condition before any ossifica- 

 tion can be perceived. Erom the bare fact therefore of the continuity 

 of the cartilage we can no more draw any conclusion respecting the 

 unity of any portion of the skeleton, than we can respecting its 

 multiple nature from the mere circumstance of the division of the 

 cartilage. So long then as no proof is furnished that the ossification 

 of the episternal bone proceeds from the true sternum, or that it is 

 identical and continuous wnth it, it appears to be unsafe to consider 

 it as belonging to the sternum merely on account of its adherence 

 to it. 



All doubts respecting the complete independency of the episternal 

 structures disappear on examining those Eodentia and Insectivora, 

 that are provided with clavicles. Thus in Coelogenys (fig. 2.) 



Fig. 2. 



y\ 



Episternal ai)paiatusof Ccelogenys paea 

 piece; c\ first rib. 



-Ep, epistcrnum ; w?, median episternal 



all three parts (central and two lateral) may be clearly recognized, 

 though the two lateral portions have become detached from the 

 middle azygous portion. Here the sternum is considerably prolonged 

 in front of the attachment of the first rib (c^, and terminates in a 

 lancet-shaped cartilaginous piece {m) which presents upon its anterior 

 surface a long keel extending from end to end, though somewhat 

 flattened behind, near the sternum. On examiniug thin sections car- 

 ried through the junction of the cartilage with the sternum, it is 

 found that there is no (^irect continuity of tissue, but that a well- 

 marked line of division exists between them, formed by fusiform 

 cells arranged transversely, and lying in a softer fibrous matrix. In 

 front of, as well as behind this line, the tissue passes into that of true 

 hyaline cartilage. To the posterior extremity of the median portion 



