176 ON THE DEVELOPMENT OF THE ANIMAL TISSUES. 



in the particular that the turbidity produced in the solution by hydro- 

 chloric acid is removed by the addition of an excess of the acid. 



2. Tendinous Tissue. The fibres of tendinous tissue are formed from 

 cells, in the same way as those of cellular tissue. 



3. Elastic Tissue. The middle coat of the arteries in embryo pigs, 

 six inches in length, contains numerous isolated cells, some of which 

 are globular, and some have an oblong form, while others give out two 

 or more branching processes of various length. At the inner surface of 

 the wall of each of these cells lies the usual nucleus with one or two 

 nucleoli. In addition to the cells thus variously modified, fully deve- 

 loped elastic tissue is also present. The branching fibres of elastic 

 tissue, which according to Purkinje, are hollow tubes, appear to be 

 formed from the cells just described. 



CLASS V. In the development of the tissues of this class there are 

 first formed independent cells, which either are round or cylindrical, or 

 have a stellate form. In the former case the primary cells arrange 

 themselves in longitudinal series, their walls coalesce at the points of 

 contact, and the septa thus formed between the cavities of the different 

 cells are subsequently absorbed, so that in place of several primary cells 

 one secondary cell is produced. This secondary cell now continues to 

 grow as the simple cells grow. In this way the fibres of muscles and 

 nerves appear to be developed. In the case of the stellate primary cells 

 the radiating processes of contiguous cells unite, and their walls be- 

 coming absorbed at the points of union, a network of communicating 

 canals is formed. This seems to be the process by which capillaries are 

 developed. 



1. Muscles. Valentin had observed that the primitive fasciculi (fibres) 

 of muscles are formed by granules arranging themselves in a linear 

 manner and coalescing ; but that the primitive fibres (fibrilbe) are pro- 

 duced by the subsequent division of the primitive bundle. Schwann 

 has remarked that the primitive fasciculi in the muscles of a foetal pig, 

 measuring three inches and a half in length, present a dark border 

 and a middle, more transparent part, probably a cavity. In this more 

 transparent part he perceived, besides some small granules a series of 

 larger oval flat bodies, which appeared to be the nuclei of cells, and 

 frequently contained one or two smaller corpuscules their nucleoli. 

 These nuclei lay at pretty regular distances from each, in the thickness 

 of the cylinder, but external to its axis. In muscles more advanced in 

 development, the primitive fasciculi present no indication of a cavity ; 

 but the nuclei remain visible for a long period, frequently producing 

 slight prominences on the surface of the cylinders. According to re- 



