102 GENERAL ANATOMY OF THE TISSUES. 



bonate of lime, and arise in different structures as incrustations of homo- 

 geneous tissues and of cellular parenchymata, as solidifying excretions of 

 calcareous matter, or as deposits of calcareous concretions. The teeth 

 are limited to the three well-known classes of vertebrata. In the 

 Plagiostomata, structures precisely similar to the teeth occur as cuta- 

 neous spines. 



Literature. Deutsch, " De penitiori ossium structura Observationes," 

 Diss. Vrat., 1834 ; Miescher, " De inflammatione ossiura eorumque ana- 

 tome generali." Accedunt observat. auct. J. Miiller, Berol., 1836 ; 

 Schwann, article " Knochengewebe," in " Berl. encyclop. Worterbuch 

 der med. Wiss.," Bd. xx. p. 102 ; Tomes, article Osseous Tissue, in 

 "Cyclop, of Anatomy," vol. iii.* 



26. Structure of the Smooth Muscles. The smooth muscles consist 

 essentially of microscopic, usually fusiform, more rarely shorter and 

 broader fibres, to which I have given the name of " contractile or mus- 

 cular fibre-cells." Each of these elements, in the mean from 0-02- 

 % 04 of a line long, 0-002-0-003 of a line broad, is an elongated cell, 

 wherein, however, no difference between contents and membrane can be 

 distinguished ; but which consists of an apparently homogeneous, often 

 finely granulated or slightly striated, soft substance, in which without 

 exception in the middle of the fibre a generally columnar elongated 

 nucleus exists. These fibre-cells are united by means of a substance 

 which cannot be directly demonstrated, into flattened or rounded cords, 

 the bundles of the smooth muscles; which are then united, by delicate 

 investments of connective tissue with fine elastic fibres (a kind of peri- 

 mysium), into more considerable masses, in which numerous vessels and 

 a relatively small number of nerves are distributed. Chemically, the 

 principal constituent of smooth muscle is a nitrogenous substance similar 

 to fibrin, the so-called muscular fibrin or syntonin (Lehmann), which, 

 from the observations that have hitherto been made, is distinguished 

 from blood fibrin only in this, that it is not dissolved by solution of 

 nitre, nor by carbonate of potass, but very easily by dilute hydrochloric 

 acid. 



* [While perfectly agreeing with Professor Ko" Hiker's general view of the relations between 

 dentine and bone, namely, that the canals in the former represent the cavities and canaliculi 

 which exist in the latter structure, we do not think that his statement of the mode in which 

 the process of calcification of the dentine takes place is correct. So far as we have seen, 

 the dentine is never developed by the immediate ossification of cells, nor do the latter take 

 any direct share in its formation. (See Quarterly Journal of Micros. Sc., April, 1852.) It 

 may be said that dentine is bone, in which, in consequence of the early disappearance of the 

 " nuclei" from the ossifying blastema, the lacunae are not formed, the dentinal tubes present- 

 ing only the canaliculi. Tus.] 



