46 FOURTH LECTURE. 



in water of all the tissues of the body ; it contains only 1. 5 

 per cent, of solid constituents, of which a part must still be 

 referred to a delicate pellicle surrounding and permeating the 

 whole. And yet the origin of the cartilage and corpus vit- 

 reum are similar. We again meet with rounded, indifferent 

 cells with a homogeneous, intercellular substance. In car- 

 tilage (Fig. 23) the latter early solidifies ; in the vitreus it 

 becomes watery and swells up, so that in a human embryo 



of four months (Fig. 46) the 

 protoplasmatic cells, meas- 

 uring 0.0104 to 0.0182 mm., 

 are separated by considera- 

 ble intermediate gelatinous 

 tissue. The latter gives the 

 reaction of mucous sub- 



man^A^ Ti5SUe ° f ^ vltre ° US b ° dy ° f 3 hU " stance or mucin, that sub- 

 stance with which we have 



already become acquainted (p. 36), as a product of the meta- 

 morphosis of the epithelial cells. For this reason our tissue 

 has already been given the name of mucous tissue. 



In the vitreus of the mammalia after birth, the formative 

 cells become arrested, and, widely separated by the interven- 

 ing gelatinous tissue, are only with difficulty recognized. 



A higher development of the gelatinous tissue is consti- 

 tuted by the so-called enamel organ of the progressing tooth. 

 The teeth, as is known, are formed and concealed in the jaws ; 

 the crown is first formed and the root last. The former is 

 covered, at its commencement period, by a cap or bell-shaped 

 structure, from the concave under surface of which the for- 

 mation of the enamel takes place. Hence the name. 



Here (Fig. 22) we meet with a net-work of delicate, nucle- 

 ated stellate cells with a varying number of processes. Some- 

 thing like a cell division ib) is occasionally seen. The meshes 

 are filled with a homogeneous gelatinous tissue containing 

 mucus. 



The same condition prevails, at an early period, in the 

 Whartonian jelly of the umbilical cord. Later, we meet, in 



