General Anatomy. 



19 



GENERAL ANATOMY. 



Although in every respect a continuous structure, the body is 

 differentiated into a large number of parts, or organs, the latter 

 being more or less individual in form, composition, or function. 

 Organs are arranged for the most part in systems, each of which is 

 concerned with some general or fundamental function, to which 

 several organs may contribute. 



In a more general way the body may be considered as an 

 assemblage of tissues. The latter are layers or aggregations of 

 similarly differentiated cells. They are of several different kinds 

 and are variously associated in the formation of organs. Being 

 structures of an intermediate position they may be considered either 

 as organ components or as products of specialized cells. 



As a body-unit a cell 

 consists of a small mass of 

 living protoplasm, contain- 

 ing a central body, the nuc- 

 leus, and surrounded or en- 

 closed on its free border by 

 a cell-membrane. The 

 nucleus is a highly organized 

 body, having an important 

 function in the reproduction 

 of the cell and also in its 

 general activity or metabol- 

 ism. It contains a charac- 

 teristic formed material, 

 chromatin, and frequently 

 also a minute spherical body, 

 the nucleolus. The chief features of a typical cell are illustrated 

 in the accompanying figure (1) of the developing ovum, the latter 

 being a single cell, noteworthy for its large size, and also one in 

 which the external form is not greatly modified, as it is in the 

 majority of the cells of the body. Its enclosing membrane, the 

 zona pellucida, by which in its natural position in the ovary it is 

 separated from the surrounding follicular cells, is considered to 

 belong in part to the latter. 



As fundamental living matter, protoplasm possesses certain 

 properties on which the functions of the body ultimately depend. 



•n.m. 



-chr. 



Fig. i. Developing ovum of the rabt it. 

 From a section of the ovary: chr.. chromatin; 

 n.m., nuclear membrane; p.f., cells of the primary 

 ovarian follicle; z.p., zona pellucida; pr., proto- 

 plasm. 



