I.] THE FROG. 147 



(3. The horny layer ; usually of a yellowish 

 colour; made up of flattened cells whose 

 boundary lines are rarely distinguishable. 

 Nuclei for the most part absent; pigment 

 granules present at intervals. 



b. The dermis ; work inwards from the epidermis ; 

 the following elements will be seen. 



a. Connective tissue ; forming the main mass, its 

 cellular elements well marked, fibres for the 

 most part in bundles. 



/?. Unstriped muscle; most marked in the deeper 

 portion where it forms a thick muscular stra- 

 tum^ lying beneath the cutaneous glands. 



y. Pigment ; deposited for the most part in two 

 well-defined strata of irregular branching cells ; 

 rarely diffused throughout the connective- 

 tissue mass. 



The above-named strata are : a superficial 

 one lying beneath the epidermis (cf. ii. <:.), 

 generally black and highly conspicuous; a 

 deeper one, immediately internal to the mus- 

 cular stratum, of somewhat lighter colour 

 than the other. 



8. Pat ; rarely present : when it is deposited, 

 like the pigment, within individual cells of 

 the connective-tissue mass. 



e. Blood vessels; inconspicuous in uninjected 

 preparations. Their cut ends may however 

 be seen among the cells of the inner pigment 

 layer ; thence vessels may sometimes be traced 

 passing up, in a pigmented sheath, towards 

 the bases of the cutaneous glands. 



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