42 ANATOMY. 



the bones are covered with a so-called fibrous membrane, composed of fibrous 

 connective tissue, named in the former case the perichondrium, and in the latter 

 the periosteum, p. In the open or cancellated structure of the jaw-bone will be 

 found some marrow. The tooth furnishes us with an example of tooth-sub- 

 stance, or dentine, of the crusta petrosa, and of the hard pearly enamel by which 

 its smooth exposed part is covered. The rings of the trachea, the larynx, and 

 the pieces of the hyoid bone are connected together by simple membrane, of 

 which the piece marked, m, is a good illustration, consisting of dense areolar 

 connective tissue ; in it will be found examples of the little lobulated masses of 

 adipose tissue or fat, /. Plenty of the loose form of areolar connective tissue is 

 also found (in many places charged with fat), connecting the different parts, 

 and surrounding and supporting them. In the junctions of the several pieces 

 of the larynx (to be exposed by dissecting the piece, c, away from the rest) 

 little joints even will be detected, united by ligaments composed of fibrous con- 

 nective tissue, and lined by synovial membranes, consisting of a basis of areolar 

 connective tissue, covered by a layer of epithelium. On examining the interior 

 of the larynx it will be round that the slit-like opening called the glottis is 

 bounded on each side by two yellowish-looking cords, the vocal cords : these 

 are composed of nearly pure yellow elastic tissue. The valve at the root of the 

 tongue, called the epiglottis, which projects over the aperture of the glottis, is 

 made up of a mixture of cartilage and elastic tissue, or yellow fibro-cartilage. 



Situated in the substance of the membrane composing the hinder flattened 

 part of the trachea, where the rings do not reach, are transverse bands of a 

 pale pinkish hue : these consist of the unstriped or simplest form of muscular 

 tissue, such as is found in the viscera generally, excepting only the heart. The 

 mass of the tongue consists of the striped form of muscular tissue, such as con- 

 stitutes the flesh or muscles generally. As shown in the dissection, this striped 

 muscular tissue is composed of bundles of soft fibres, which are collected into 

 definite masses, or muscles, such as are marked, m, m, m, one radiating from 

 the lower jaw throughout the whole tongue, another passing from the lower 

 jaw to the hyoid bone, and others passing in form of three bundles from various 

 points of the hyoid bony apparatus to different parts of the tongue, one reach- 

 ing to its very tip. 



Entering the tongue at its side, near the root, is one of those bloodvessels 

 which are called arteries, a ; and passing out from the tongue near it is a vein, 

 v ; the branches of both being traceable far into the tongue, where they finally 

 end in a common uniting network of those minute vessels, invisible to the 

 naked eye, named capillaries. All the blood of the tongue in the natural state 

 is contained within these three kinds of tubes or vessels. There are also absorb- 

 ents belonging to the tongue, but these it is impossible to see. Two nerves, n, n, 

 likewise penetrate the tongue, one of which, the hinder one, sends its fine 

 branches into the muscular substance, being a muscular nerve ; whilst the 

 other, the forward one, gives off twigs which advance through the muscular 

 substance to the surface of the organ, and supply the soft moist membrane or 

 skin which everywhere covers it in the natural condition. 



This membrane or skin is a mucous membrane. It is indeed only a part of 

 that extensive mucous membrane which, commencing at the mouth and nos- 

 trils, passes from both points backwards into the pharynx, and thence into the 

 larynx, and along the windpipe and its branches into every part of the lungs, 

 and also down the gullet, along through the stomach and the rest of the ali- 

 mentary canal. On the under side of the free part of the tongue, where it is 

 continuous with the gums, this covering membrane is smooth, but on the fore 

 part on the top of the tongue, pa, it is covered with little eminences called 

 papillcE, or is papillated ; further back it has larger papillae, and is also provided 

 with mucous follicles and glands, little organs which secrete or form the mucus 

 or general moisture of the mouth. The saliva is formed by more complex 

 secreting glands, of which one called the sublirigual gland, g, is shown in the 

 dissection. It is a lobulated mass from which many short tubes or ducts pro- 

 ceed and enter a large tube or duct, d, beneath, which comes itself from the 

 submaxillary gland, not shown in the figure, and opens on to the surface of 

 the mucous membrane beneath the forepart of the tongue, where it discharges 

 its salivary secretion or saliva into the mouth. These and all other secreiina 



