TISSUES OF THE BODY. 357 



the finer ramifications the state of things already seen in the smaller 

 mucous glands. The more considerable and terminal passages, however, 

 acquire a tougher internal tunic, rich in elastic -elements, which is 

 enveloped in the external coat. Between these two layers there is inter- 

 posed, further, in one class of glands a muscular sheath, consisting, when 

 only slightly developed, of longitudinally arranged unstriped fibre-cells, as 

 in the mamma and Cowper's glands. When more highly developed it is 

 made up of an external longitudinal and internal transverse layer, to 

 which may be added another still more internal of longitudinal fibres (vas 

 deferens). The tunic situated internal to these, formed of connective- 

 tissue, is gradually converted into a mucous membrane clothed with 

 cylinder cells, and in it again minute mucous glands may appear (biliary 

 and pancreatic ducts). 



198. 



Turning now to the individual glands, the following points may be 

 borne in mind : 



1. Among the tubular glands of the human body may be reckoned 

 Bowman's of the regio olfactoria, Lieberkuhn's of the small intestine, the 

 so-called follicles of the large intestine, the peptic and mucous glands of 

 the stomach, and the glands of the uterus. These all consist of follicles 

 of varying length, formed of a simple membrana propria. Their length, 

 which depends on the thickness of the mucous membrane, ranges from 

 0-2256 to 2-2558 mm. and upwards. In breadth they differ consider- 

 ably; in Bowman's glands the diameter being -032 3-0 '05 6 4 mm., in 

 LieberJcuhn's 0*0564 mm., the large intestine 0-0564-0-1128 mm., and 

 those secreting the gastric juice 0'0323-0'0457 mm. 



The number of these glands is often very considerable, so that they may 

 cover the whole surface of the mucous membrane when crowded together, 

 as, for instance, the follicles of Lielerkuhn of the cat (fig. 350.) The 

 tubes usually remain undivided, but in many glands, as those of the 

 stomach and uterus, each may be 

 split into two or three branches. 

 The cells contained within them 

 are partly flattened and round, 

 partly cylindrical. 



Among the convoluted glands 

 we have the smaller and larger 

 sudoriferous organs, the cerumi- 

 nous glands of the ear, and the 

 tubules occurring in the conjunc- 

 tiva at the edge of the cornea 

 in many mammals. It is seldom 

 that, as in the latter situation, 

 they possess a simple membrana 



propria. In most the Wall is Fig. 350. Lieberkuhn's glands from the cat (a), sur- 



stronger, this membrane being > mounted by intestinal vim (6). 



again enclosed within a layer of connective- tissue, between which struc- 

 tures muscular elements may be interposed as a middle tunic, e.g., the 

 large sweat glands of the axilla. In this manner. the walls may attain a 

 thickness of 0'0045-0'0094, or even 0'0135 mm. The breadth of the 

 very long tubules of a convolution varies from 0'0451 to 0'0992, or even 

 0-1505 mm., and that of the whole of the latter from 0'2 to 6 '7 mm. 



