STRUCTURE Or GLANDS. 



257 



glands of the skin, other than the sudoriparous and sebaceous 

 glands are encountered.* 



[ 423. The progressive development of the last form of 

 gland is observed in the lachrymal, salivary and lacteal glands, f 

 in all of which a greater amount of ramification, an increase in 

 the quantity of vesicles and racemes produced, and a greater 

 degree of separation of the individual parts into lobes, are 

 observed. The lachrymal gland of man, of mammals and of 

 birds, exhibits terminal cells, which in the latter class are 

 large and conspicuous ; in man, on the contrary, they are 

 much smaller. The salivary glands of man are formed in the 

 same way (fig. 257). The cells of the terminal vesicles of 

 the parotid may still be readily 

 filled with mercury in young sub- 

 jects ; they are two or three times 

 smaller than the finest pulmonary 

 cells, measuring no more than from 

 the 30th to the" 60th of a line in di- 

 ameter. The structure of the pan- 

 creas is similar, and the terminal 

 vesicles of this gland are very easily 

 filled with mercury or with air, in 

 birds especially, measuring when 

 thus distended from a 50th to a 

 30th of a line in diameter ! J The 

 mammary glands in the ornithorhyn- 

 chus are extremely simple, and ex- 

 hibit the commencement of a series 

 of evolutions that end with the 

 most complicated raceme ; the structure here consists of a con- 



* To this number belong, for example, the musk bag, and the anal sacs 

 of many animals the marten, the otter, &c., which exhale a peculiar 

 odour or stench. They are, in fact, extensive involutions of the skin, of 

 simple structure, occupied internally by shallow pits ; these structures 

 might be regarded as simple follicles, which, upon occasion, however, 

 may become more complicated, as they do in the anal sac of the hyaena, 

 Linple, which is made up of several racemes clustered together. 



t On the structure of the glands in general, and of each of those men- 

 tioned in particular, see the work of M tiller, and the Elementary Treatises 

 on Anatomy of E. H. Weber and of Krause. 



J The pancreas of fishes has been very commonly quoted as affording 

 an example or type of the successive evolution of glands from the simplest 



Fig. 257. A very small 

 piece of the parotid gland of 

 a new-born infant, filled with 

 mercury and magnified five 

 diameters. After Weber. 



