THE SKIN. ITS PAPILLA AND GLANDULE. 



241 



type of this more complex glandular apparatus is presented to us in those small 

 bodies peculiar to the duodenum, which are known as " Brunner's glands." (Fig. 

 29.) The terminal vesicles of these racemose clusters are loaded with cells 

 formed in their interior, the aspect and mode of production of which are quite 

 different from those of an epithelium. This will be better understood from the 

 succeeding figure (Fig. 30), which represents one of the terminal caeca of the 

 liver of the Crab j this is seen to be crowded with cells, which not only line its 

 internal surface, but fill its cavity ; and the cells are observed to originate in 

 the midst of an indistinct granular matter that occupies the deeper portion of 

 the follicle, increasing in size and completeness as they are pushed towards its 

 outlet by newer growths beneath. In most glands, an unlimited production of 

 cells appears to take place continuously within the same follicles ; the cases in 

 which the follicles shrivel and dwindle away, when they have once opened them- 

 selves and discharged their contents, being comparatively few. All glandular 

 structures require a copious supply of blood, to fur- 

 nish the materials of the secretion which they elimi- Fig- 30 - 

 nate ; and this is afforded by a minute capillary ^ $ 

 network, which closely surrounds the follicles or 

 vesicles, but which never penetrates their interior 

 (Fig. 31.) 



Fig. 81. 



O nc of the hepatic cseca of 

 .#? (Cray fish), highly magnified, 

 showing the progress of development 



of the secreting cells from tlie blind 



Capillary Network around the follicles 

 of Parotid Gland. 



236. The Skin. Like the Mucous Membranes 

 with which it is continuous at the nose, mouth, 

 anus, and the other orifices of the canals which 

 these line, the Skin may be considered as composed 

 of three elements; namely, the complex fibrous 

 tissue, which, with bloodvessels, lymphatics, and 

 nerves makes up the Cutis vera or Corium ; a layer 

 of Basement membrane investing this, and an epi- 

 thelial investment of peculiar thickness and tena- 

 city, which is known a. i^ Epidermis or "cuti- 



Cle. - Ihe Substance OI the Cormm IS principally 



composed of White fibrous tissue, which is arranged 

 in a reticular manner ; the texture being very fine 

 and close near the surface, but more open in its deeper layers, where its areolse 

 become occupied with clumps of fat-cells, and where it passes, without any dis- 

 tinct line of separation, into that of the subcutaneous Areolar tissue. With 

 this white fibrous tissue, a small proportion of yellow or elastic fibres is usually 

 intermixed ; and this proportion is greatly increased in those parts of the skin 

 which are subject to occasional distension, and especially in the integument sur- 

 rounding the joints. ^ The Cutis, however, not only possesses elasticity; but is 

 also endowed with vital contractility, which is peculiarly manifest in particular 

 parts, especially under the influence of cold or of mental emotion ; producing 

 16 



cesgive stages, are shown separately 



at a, 6, c, d, e. 



