126 THE CONNECTIVE TISSUES, BY A. ROLLETT. 



either cells or their remains in the granular masses which occur 

 in the lacunae, and which were long ago observed by Schwann 

 in decalcified bones. 



Sharpey* has described certain fibres which come into view, if 

 we attempt to isolate the lamellae of a decalcified flat or long bone, 

 as constituting a special morphological constituent of osseous 

 tissue. They run in planes which lie nearly perpendicular to 

 the surface of the lamellae, and appear as pointed processes 

 projecting from the surface of those lamellae that have been 

 torn away from their attachments ; whilst in the adjoining 

 lamellae the foramina may be recognised from which these 

 so-called Sharpey's or perforating fibres have been withdrawn. 

 As H. MuUerf showed, they occur in man in the bones 

 developed in periosteum, and may there attain a length of as 

 much as three millimeters, whilst their thickness varies from 

 O002 to O005, sometimes even to 0'015 millimeters. 



The perforating fibres are calcified rods, which, prior to the 

 formation of the bone lamellae they traverse, extend as bridges 

 between the embryonic bone and the surrounding connective 

 tissue, through the formative layers of the bone lamellae ; with 

 increasing thickness of the lamellae they first elongate and then 

 calcify. When a portion of these fibrous bundles remains un- 

 calcified, they form, according to H. Miiller, when the bone is 

 dried, the perforating tubes described by Tomes and De Morgan. 



KollikerJ has called attention to the wide distribution of the 

 perforating fibres, especially amongst Fishes. 



DEVELOPMENT OF BONE. Embryological investigation shows 

 that almost the entire bony skeleton of vertebrate animals is 

 developed from a cartilaginous skeleton which is laid down at 

 an early period. This was originally held to be the mode of 

 development of all bones, till Sharpey and Kolliker demon- 

 strated that several of the cranial bones originated directly 

 from connective tissue. These constitute the investing bones 

 of the primordial skull. It has now been known for a con- 



* Quain's Anatomy, sixth edition. 



t Wiirzburger naturwissenschaftliche Zeitschrift, Band i., p. 296. 



I Ibid., Band i., p. 306. 



