136 E. A. SiHaFER. 



If any of the elastic perforating fibres are present in the 

 section they are brought very clearly into view, being stained of 

 a dark-red colour;^ whereas the general substance of the bone 

 is merely tinted of a rosy-red, and the white perforating fibres 

 are hardly coloured at all. It is not difficult in this way to 

 make out the number and disposition of those of the elastic 

 variety. 



It is seen, in the first place, that they vary considerably in 

 number in different parts. In some sections it is difficult to 

 make out any, in others they are more frequent but run singly, 

 and can only be traced for short distances, whilst in some other 

 sections, as for instance in the one from which fig. 1 Plate VII, 

 is taken, they are very numerous, and run both singly and in 

 groups, generally but not always distinct from those of the white 

 variety, and, like these,^ being always found piercing the cir- 

 cumferential and interstitial lamellse, never those of a Haversian 

 system. They are also often traceable directly from elastic fibres 

 in the periosteum. 



The groups, like those of the white bundles (Gegenbaur), 

 often run alongside blood-vessels (Haversian canals), which pass 

 in from the surface of the bone, and some may even appear to 

 pass into or emerge from such a canal. This may have given 

 rise to the idea that the perforating fibres were to be found 

 piercing the lamellse of Haversian systems. It should be noticed, 

 however, that these canals near the periphery of the bone are 

 frequently not encircled by systems of concentric lamella?, but 

 merely lie between the circumferential lamellse. 



The individual elastic fibres are always, in the human subject 

 at least, very much finer than the white perforating fibres. 



Like the elastic fibres in connective tissue elsewhere, they con- 

 stantly tend to branch and to unite by their branches with 

 neighbouring fibres. Their course is never straight but wavy 

 and often irregular through the bony substance ; indeed, they 

 are sometimes singularly curled and contorted. This fact with 

 regard to the elastic fibres in bone casts doubt upon the notion 

 that in ordinary connective tissue the elastic fibres in their 

 natural condition always pursue a straight course, an opinion 

 which seems to have been based chiefly upon the examination 

 of stretched specimens. 



III. Origin of the Intercrossing Fibres and of the Perforating 



' My attention was first drawn to lliis by Mr. W. Kushton Parker, one 

 of tlie students in my class at University CoUefre. 



' lianvier, 'Traite Technique. So far as my observations have pone (hey 

 lead to an entire disagreement with Gegenbaur's statements and fii^ures as 

 to the relation of the perforating tibres to the lamella of the Haversiau 

 systems and to the lacunce. 



