THE OSSEOUS SYSTEM. 307 



be isolated, — the best proof, that everything which thus 

 presents itself in an isolated form, is not necessarily a mor- 

 phological unity. 1 ] 



§ 92. 



The Periosteum. — Among the soft tissues appertaining to 

 bone, the periosteum is one of the most important. It is a 

 more or less transparent, slightly glistening or whitish yellow, 

 vascular, extensible membrane, investing a great part of the 

 surface of bones, and contributing most importantly to their 

 nutrition, by the numerous vessels which it sends into their 

 substance. 



1 [It is of very great importance in histology to keep in mind the caution ex- 

 pressed in the last paragraph of the text (see below, note § 101), which applies as 

 well to optical as to chemical distinctness. 



Tomes and De Morgan assert that both the lacuna and canaliculi have parietes, 

 which are manifested by appearances similar to those observed in the dentinal tubes. 

 They sometimes found the lacuna and canaliculi filled up to a great extent with solid 

 matter, so as to leave only a small space in the centre. 



An important modification of the lacuna? is described and figured by these authors 

 (1. c, p. 8) in the circumferential laminae. Elongated tubes pass, in bundles or singly, 

 more or less obliquely from the surface towards the interior of the bone. When 

 long, they are sometimes bent once or twice at a sharp angle. They have parietes, 

 and are connected laterally with the canaliculi. They occur irregularly in the cir- 

 cumferential laminae, and in these only. [Similar tubes exist in the cementum of 

 the Teeth.] 



We can confirm Messrs. Tomes and De Morgan's statement that the nuclei may- 

 be found without difficulty in recent bone, and they may always be brought out with 

 great distinctness by the action of dilute hydrochloric or strong acetic acid. This is 

 especially the case in young bone. In old bone we have frequently been unable to 

 discover them. Tomes and De Morgan, however, state that the nuclei are visible in 

 sections of a fossil bone (supposed of a Pterodactyle) in their possession. 



Another peculiar condition of the " lacunal cells," described by these authors, is their 

 ossification. They found the light and spongy bones of old people to yield, if broken, 

 a white powder, which was composed of large cells detacbed or united into masses. 

 They are spherical, and contain a dark granular nucleus, which is surrounded by a 

 thick transparent wall. Similar cells may be found adherent to the walls of the 

 Haversian canals and cancelli ; and in this case their nuclei have assumed the form of 

 lacuna, and the canaliculi of adjacent lacuna advance into them. Similar cells may 

 be found in most preparations of adult bone (1. c, p. 12). 



We must confess that we doubt the assumption of a lacunal form by the "nucleus" 

 in these cases. We have repeatedly examined these bodies, but if the nucleus was 

 visible at all, we found it unchanged, and often adhering to one side of the lacuna. 

 Again, it is questionable whether they may not rather be compared to the globules 

 of dentine than to cells. — Eds.] 



