Section I.
I
OP THB GLANDULAR aTSTEM.
I
The term giand has !>c«n »o very vaguely and friV^ oonvcUy us«d liy anatomists, that it h ditficult to d«6ne' its exact siguilicatjoii, or to specify' the organ!* to which ' it should be applied. Parts, which are the moit diss!-' milar in structure, connexion, and fiinctJon, such as the pineal, tlic thyroid, the thymus, the renal, and the lym-' phatic glands, have been indiscriminately classed toge- ther under the above denomination ; and by this com- mon name they are also confounded with organs of a truly glandular character, as the liver, salivary glands, &c. This arrangement is highly objectionable, because H ' misleads by implying a similarity of organization in ports which have not the slightest resemblance to each other.
The most comprehensive definition is that which ad- mits, imder the name of gtand^i, all those organs which secrete any fluids from the blood ; but this is too exten- sive, as it confounds together the recrementitial secre- tions, as those of the serous and synovial membrancfl, with the cxcremcntitial fluids which arc derived from mucous surfaces, or from the proper glands. Some writers have thought that a ruimded form was essentia]
DKFIKITIOK OF OtAKD. 3129
to the character of a gland ; this restriction is not, how- ever, well founded.
It hiLS been judiciously observed, that in order to dis- linguish the glands from all other organs, which they may resemble in their form and in their apparent tex- ture, it is necessary to pay particular attention to their connexions. Bichat considers a proper excretory duct as es$ontinl to the character of a gland. Ilease hits adopted this idea, but he has committed a serious error by class- ing with the proper glands the lymphatic glands, which he supposes possess excretory ducts.
The tL-rm gluiid ought to be applied to those organs wliich are composed essentially of the union of the mu> couH and vascular systems, and which are provided with ducts, hanng usually a ramified disposition, and termi- nating on the internal or external cutaneous surfaces. This definition entirely, and, as I believe, properly, ex- cludes the following bodies: the pineid, the pituitary,, the thyroid, the thymus, and the renal glands ; also the spleen, and the lymphatic glands.
, It is extremely difficult to determine where the line of demaxcation should be drawn between the mucous folli- cles and the glands. It has already been stated, that among the former, some are insulated and solitary; others aggregated or grouped together ; and, lastly, that some are compound, or composed of the union of several bags, which have cither a common orifice, or several opeoings. It is here that the dtlliculty exists ; for there is no valid reason why the molar glands, the tonsils, and Cowper's glands, should not be ranged among the proper glands. Tlie prostate and the vesiculsc seminales are still more closely allied to the glandular organs.
The most perfect glands are, the lachrymal, the paro-
330
ORQANIZATION OP GLANOti.
tid, the submnxUlary, and the subling;ual ; the paBcreaa^ the liver, the kidnej-s, the testes, (ind the mammie. Th« ovaria of the female Imve also been included by Meckc und Beclard ; but these bocUes bear »o little reu^mbtiuica: in structure or function to the preceding organs, that tliey cannot properly be u^imiUted with them.
The extemxd form of the glands, although it presents: many indiv-iduol varieties, is usually round or 0^*81, particularly in the early periods of life. Many of thenii consist of small lobes united to each other by a cel^ lular, or even, as in the parotid gland, by n tibrous tiMuej these arc called glandttia conghmemta. Tli lobulated arrangement extends to the interior of sc glands, as the lachrymal and salivary; it is also ob-yl served, but not so distinctly, in the mamuiffi. The taaticles ha'c a lobulated appearance, hut of a diftj ftfCQt character, which is owing to the existence rm ligamentous septa. The liver is lobulated ou llie uxi ' temal surface only, and the kidneys mvn;ty in the fcetus.
1 .,1 ^ Sbction 11.
OttGANIZATION OF TRB GLANDS.
Thb glands, which are amongst the most vaxcular parts of the body, present variations as to thp qiiantitv of blood which each individually receives ; the kidney*,' however, suqiass uU the others in tlic great capacity of > their arteries. The length, the courttc. and the niod« ot ■ distribution of the blood>ve.s$els arc equally nirinhlc.< They either penetrate the surtace of the organs by Hevt>>
VKSSE1.S, NBRVBS, SXCRBTORY DUCTS.
raJ brnnches, as in the Kslivary glands ; or, as most' usually happens, Ihey enter in single trunks at fisimreR;) which are placed, as in the liver and kidney, in liic least exposed part of the gland. The ditTc-rcncc in the relative capacity of the arteries and veius^ which is so' striking eUewhvre, is very little marked in the f^ands i1 because a cunsidernble part of the blood is changed into llie secreted fluid, and is carried away hy the excretory ducts. The lymphatic vessels are numerous, and in some instances, as in the testis, they are very larg«.
The nerves arc vory small, and often constitute' plexuses ; Uiey are in most instances derived from thei system of the sympathetic, hut in part tirom the cerebro-< spinal axis. ■■"{
' Every gland has an excretory opening, which is either tntnple, or the termination of a canal which is ramified' in the interior. The little orifice of the sebaceous or' mucous follicles, which conveys to the external surfac«' the secreted fluid, is the most simple example of an excretor)' duct, and may be received as the type of the entire class. Some of the more complicated of the mucous follicles, as the amygdalse and Cowper's glands, have excretory canals ; but they are short and are not ramifled. In the prostate and vesiculie semi- nales the cmunctories arc still raorc developed. The ramified and intricate canal to which the name of ex> CTCtory duct is more particularly applied, is, however, only possessed by the proper glands. Each of these tubes begins by very fine rooU wliicb unite together like Ifae branches of veins, and ultimately constitute one or more large duels, which issue from tlie organ, and open obliiiuely on the adjacent part of the mucous membrafie-
■tW'»'
r
333
^'1 SBSBBVOIRS OF 0LAND9.
P
Thw |^e<!«l^Rr mode of l«mmation 'allwws' ftie ff<fttr off tlic fluids from the gkud, but not in the retrograde direction.
■ji/The duct of tJie kidney, the ureter, h(^ns from enlarfred receptacle, called the pelvis ; it nfterwards te minutes in a capacious reser*oir, named the urins bladder. The hepatic duct has likewise connectwi vritn i(, a peculiar reservoir, vestcula feUts, in ■which the bile is collected, and where an iibsorption of the watery parts of that humour takai place. It has also been; said by many anntomiHts, even in the present days thi the vesiculte seminales arje receptacles for the Bcmei*; and confiequently that they have the same relation to tiiiii testicles that the gall bladder has to the liver; but Ihidj statement is incorrect, as the vcsiciJa arc undout)tcdI^] proper secreting bodies. ITie excretory tubes of tf« mamma?, the galactophorous or lactiferous duels, remarkably enlarged towards their extremities, so as l<f^ retain the milk till they are forcibly extended ; and iri ' this manner thej" serve the office of a reservoir by ceiving the secreted fluid.
The excretory ducts consist of a mucous membrane,' which gradually becomes thinner i» it penetrates into their ramifications. This membrane is covered, in m<M' instances, by a dense and fibrous texture, which Is seen in tlie parotid duct, in the hepatic ducts, in the ureter^ vas deferens, &c. ; in other ducts, as tlic lactifrrous, th^ surrounding structure is of an erectile character. '
The constituent parU are joined to each other by cellular ti.ssue, which is subject to considerable variatioti with respect to its quantity and disposition in different glands. Each of these organs is also invested by tt
MINUTC STRCOTCOB OF GLANDS. 333
proper membrane, which is either of a cellular or fibrous duuacter. In some instances, as in. ithft liver and the testicles, there is an ad<litional serous coverinR, ,: The opinions of anatomists concerning tlic minute structure of tlie glands, have for a long lime bevn in- Buenced by the culuhrated Uieorieiii of Malpighi and R^iyRch. The fonncr thouffht that there were small ve»iclc» or follicles, placed between the termination of the secreting ve«sel» and the commencement of the excretory tubes, in which the last vascular ramifications were placed. This doctrine was received till Huysch, wIki wa.H 6o JuKlly di&lingui»t)ed for the success and delicacy of his injections, called it in doubt. This skil- ful anatomist contended tliut ttiese supposed vesicles coim lUBtcd altogether of an interlacement of minute ^'csseU, in w;hich the last terminations of the arteries were con- tinuous without inflbrruption with the roots of thia ejtcretory tubes. According to the former hj'pothesU the gland is nothing more than a masA of follicles ; whilst according to the latter, it Is only an exhnhmt membrane, folded and doubled on it»elf a great number of lim&s.
It is almost impossible to decide between these con- flicting statements, in consequence of the complicated structure of the gkndular organs. There is, however, reason to beliuvu that twth Malpighi and Ruysch applied their theories too exclusively, for we can scarcely suppose that such dissimilar bodies as the pancrvas und kidney, possess exactly the same kind of texture. On the whole the balance of e%'idence turns in favour of the existence of follicles. 'ITiis assertion is supported by an extended examination of the glands in the inferior animals, which proves that these organs are composed of canals
334
FUNCTIONS OP GLAKOB.''***
which, whether simple W compountt. begin from ml d« sacs, and are surrounded l»y numerous blood-vessel*^ The ty}pe of the glandukr formation h exhibited in th^ simple mucous glands, which consist of single sacks or follicles. In order to comprehend the structure of the most compound gland, we have only to figurv to ourseh'eti thcM 8&ck« prolonged and ramittL-d, wtUi their branches inter- laced with thofic of the btood-veKsel^, but without there ever being a direct communication between the san- guiferous ves-scls and tlie excretory ducts.* In admit- ting the general truth of this doctrine, we must still recollect that Ruysch is correct in stating that each glandular grain, and aLio ibc entire gland, consists of the mixture and interlacement of delicate veflAels with the origins of the excretory duct ; l«it he is wrong in saying that the excretory utbes are the contintiation nf the arteries. The efforts of minnte injection an4 nf carefiil inspection, ri-ndor it probable ihut the opinion of Malpighi applies more piirticularly to tlie granulated glands. Such mn the parotid and the pancreas ; and that the lltcory of Ruyscli extends to those organs which,-, like the liver, the kidneys, and the testes, are providc^f with a more evident -asculur nod tubular structure. '
Sbction III.
ponctions op tur glands.
The functions of these organs can only be rvgnrdv^l
in a very general manner, because each glaud has Ra^J
■It
• M<dM>l, Minud d'Anat L L p. $U.
INPLUBNCB OF NERVOUS POWRR.
especial use in the economy, the history of which bu* longs to physiology. Tlie glanduliur socrctious are, like all others, derived from the blood ; so ttmt thejr are only peculiar by their mode of sepnration, and by the compound nature of their chemical analysis. It is impossible to penetrate into the wonderful mechanism of secretion, by the operation of which, such totally different fluids, as the Mdiva, the milk, the semen, and the urine, are all formed from the blood. It is useless to attempt an explanation by physical or by chemical eausen exclusively. That chemical actions must take place IB certain, but they are chemical actions which are caused and regulated by the principle of life, so Uiat they cannot be imitated by art. The extent of our knowledge only inform^i us, that the materials of the glandular liecretionii are in all instances except one, that of the bile, furnished, by tJie arterial blood ; that in the extreme divisions of the arteries, the secreted fluid, whatever it may consist of, is separated from the cir- culating fluid ; that it afterwards is conveyed into the commencement of the excretory duct, where it becomes apparent to the senses ; and, lastly, that the residue of tlie blood, now altered in its character, is returned by means of the vein.s.
The power of the nervous system has a most impor- tant influence on glandular secretion. Thus wc leam ftom common obser'ation, that the emotions of the mind, which act on the glands tlirough the medium of the brain and ucn'cs, may either increase, diminish, or altogether suspend the secretion of any glandular fluid. And tigain, it has been proved by the experiments of Mr. Brodie and Dr. W. Philip, that the division of the nerves belonging to a secerning organ deranges or
m
DEVELOI'MBN^.
destroys its power. It has also been ascertained, that llic fipplicaliuii ut' a ligature lu thv veins uf a gland, conHidcrably augments the quantity of its secretion.
The development of the glandular system in the human embryo, corresponds in many essential points with the permanent organi7.ation of the inferior animidK. This curious fact is illustrated in the fonualion of the excretory canal, which in the commcuccment is loose and floating, as it is in insects ; and at a rather more ad^-anced period the glands are lobulated, as they Bfe i^ the arachnides and crustacea. These organs u^ . generally very targe in the fcetus and infant ; but as they afterwards remain nearly stationary in size, aaJ, OS the hulk of other parts of the body is increased hy growth, their rcktivc 'proportion is considerably diipi,. nished. The testes change their situation previgus lo birth, und at the period of puberty they are grendy developed ; and at the same time tn the female, the, , mammx are ver)* much increased in size and fulness. After the CL-,ssation of menstruation, the latter glaud« become smaller, and occasionidly indurated orschirrou»; and in old men tlie testicles are similarly affected.
or THR CARTILAG19.
b ■II
CHAPTER SIXTH.
OF niE CARTILAGINOUS SYSTEM.
.1
-J*
Caktilaoe is distingiiished from every other texture. by' Its pearly whiteness, firmness, great elasticity and, smoothness. When divided it appears to be homoge-, ncous, and to have neither fibres nor laminsc, but by prolonged maceratioD a fibrous structure can be demoQ-^ strated.
Anatomists have generally comprehended, under the ■ term of cartilage, parts which exhibit many variations in their structure. Thcsu differences which have been long remarked, induced Bichat to divide tlie cartilagin- ous bodies into cartilages and fibro-^arlilugvs ; and as this division seems to be well founded, I hove adopted it in the classification of the Bolids. In accordance with this arrangement, I shall only include under the term of cartilaginous system, the cartilages which cover the ends of tile hones in thu moveable arlJculatioDS and those appended to the ribs. The cartilages of the nose, the ear, the windpipe, Sic, which partake of the properties of true cartilage and of ligament, will be considered after the f)hrou.s organs have been described.
888
ARTICUI.AR CARTILAOE*.