86 GENERAL ANATOMY OF THE TISSUES. 



the nose (proboscis of the Pig and Mole, os pranasale of the 

 Sloth), in the tongue (os entoglossum of Fishes and Birds), in the 

 respiratory organs (laryngeal, tracheal, and bronchial bones of 

 many Birds), in the sexual organs (penis-bone of Mammalia), in 

 the osseous system (ossa sterno-costalia of birds and some 

 mammals). In the Invertebrata true bones are never found, 

 being, in them, replaced by the so-called calcareous skeletons, 

 which principally consist of carbonate of lime, and arise in 

 different structures as incrustations of homogeneous 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 

 cutaneous spines.] 



Literature. — Deutsch, ' De penitiori ossium structura Obser- 

 vationes/ Diss. Vrat., 1834; Miescher, 'De infiammatione 

 ossium eorumque anatome generali.' Accedunt observat. auct. 

 J. Muller, 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. 1 



§ 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 muscular fibre-cells/' Each of these elements, in 

 the mean from 002— 004'" long, 0-002— 0-003'" 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 Avithout exception in the 

 middle of the fibre a generally columnar elougated nucleus 



1 [While perfectly agreeing with Professor Kblliker'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 dinct share in its formation. (See 

 Quarterly Journal of Micros. Sc, April, 1852.) It may he said that dentine is 

 bone, in which, in consequence of the early disappearance of the " nuclei" from the 

 ossifying blastema, the lacuna arc not formed, the dentinal tubes presenting only 

 the canaliculi. — Eds.] 



