ccxxvi DUCTLESS GLANDS. 



or, at any rate, outside the mucous coat, there is in some ducts a deposit of 

 non-striated muscular tissue. The epithelium is usually composed of 

 spheroidal or polyhedral cells at the commencement of the ducts, and is 

 columnar in the rest of their length, though sometimes flattened or scaly, as 

 in the mammary gland. 



DUCTLESS OR VASCULAR GLANDS. 



There are certain bodies which have received the name of glands on 

 account of their resemblance in general appearance and structure to the 

 ordinary secreting organs. They differ, however, from the latter in the fact of 

 their possessing no ducts for the discharge of secretion ; so that the products of 

 secretive action, if finding any outlet, are compelled to do so by rupture, by 

 filtration through the tissues, or by re- absorption into the circulating 

 current. The bodies in question have been termed " ductless " for this 

 obvious anatomical reason : and " vascular," on certain physiological or 

 theoretic grounds, as they are supposed to effect some change in the blood 

 which is transmitted through them. 



To this class belong the following bodies : the spleen, the thyroid body, 

 thymus gland, suprarenal capsules, pituitary body ; and, according to 

 various authorities, we ought to place in the same category the solitary 

 closed follicles of the stomach and intestines, the Peyerian glands, the 

 follicular glands at the root of the tongue, and also the lymphatic glands. 

 The peculiar structure of each of these organs (except the lymphatic glands, 

 already treated of) will be considered in its proper place in that portion of 

 this work which is devoted to special anatomy ; and we have here to give 

 only a general outline of those structural provisions which are, with more or 

 less modification, common to them all. 



The following may be taken as a general account of the mode in which 

 their constituent elements are arranged. The form of the gland is deter- 

 mined by a fibrous, and in some instances dense and firm, investing mem- 

 brane, which in the larger organs is furnished with prolongations projecting 

 inwards as septa, giving considerable firmness to the texture, and either 

 forming loculi or rounded cavities within them, or merely leaving spaces 

 between the septa, in which the peculiar substance of the gland is placed. 

 The investing membrane consists of both white and elastic fibres, in vary- 

 ing proportion, and, in many instances in the lower animals, of non-striated 

 muscular fibres. Each gland is abundantly supplied with blood-vessels, 

 both arterial and venous ; the former commonly dividing frequently, but 

 entering into no anastomosis until they have arrived at their ultimate rami- 

 fication in a capillary plexus ; the latter (the veins) are usually large, valve- 

 less, and in some situations appear dilated into sacs ; but this appearance 

 has been questioned. Lymphatic vessels, proceeding from lacuuse within 

 the gland, and nerves, exist in very varying proportions. 



The blood-vessels as they pass through these glands are in some cases 

 closely surrounded by a peculiar pulpy substance, varying in amount and 

 colour at different periods, but generally existing in considerable quantity. 

 This pulp consists of corpuscles, granular matter, and fat-molecules. The 

 corpuscles are of very different kinds and vary widely in size ; some, and 

 those are the best established, resemble lymph, chyle, or pale blood- 

 corpuscles ; others, free nuclei ; some, of more questionable existence, are 

 said to be large compound cells, containing in their interior globules closely 



