THE ANATOMY OF HUMANE BODIES , WITH FIGURES DRAWN AFTER THE LIFE By some OF THE BEST MASTERS in Europe , And Curiously Engraven In One Hundred and Fourteen Copper Plates , ILLUSTRATED WITH LARGE EXPLICATIONS , CONTAINING MANY NEW Anatomical Discoveries , And CHIRURGICAL OBSERVATIONS : TO WHICH IS ADDED AN INTRODUCTION EXPLAINING THE ANIMAL OECONOMY . WITH A COPIOUS INDEX .

BY William Cowper .

THE Contemplation of Humane Bodies is doubtless one of the most Diverting and Noble Amusements , in which a Philosophical Mind can employ it self . The Structure , Contrivance , and Disposition of the Parts are Astonishing , and we can hardly desire more plain and convincing Proofs of the Wisdom and Providence of the Author of Nature , than what may be deduc'd from this Source . How surpizing are the Discoveries which the Happy Industry of the present Age has made in the Animal World : The Doctrine of the Circulation of the Blood ; the Vnity of the Veins and Arteries ; the Origin and Distribution of the Chyle and Lympha ; the Ovaria in Females ; the Embriunculi in the Masculine Seed , are equally certain and amazing ; besides a Multitude of other Curious Observations we Daily make by the Help of Microscopes , Mercurial Injections , and such like Methods .

These are sufficient Motives to induce all Inquisitive Persons , and Lovers of Natural History , to the Study of Anatomy ; but all Professors of Medicine are more immediately concern'd to be Acquainted with it ; this being little less than the Basis and Foundation of their Art . Without a due Knowledge of the Animal Mechanism , I doubt all our Attempts to Explain the Multiform Appearance of Animal Bodies , will be Vain and Ineffectual , and our Ideas of the Causes of Diseases and their Symptoms , as Extravagant and Absurd as those of the Chinese and Indians ; nay I am afraid the whole Art of Physick will be little better than Empirical .

But if the Knowledge of our Bodies do's so much conduce to advance true Philosophy and Medicine ; it is not less required in the Practice of Surgery : In this Case it seems not meerly convenient , but absolutely necessary ; I mean so far as concerns the External Parts , since the Artist here , do's not as in the former Instances , Acquiesce in Contemplating his Subject , and the Manner how it is Affected ; but is often oblig'd to Perform some Difficult , and perhaps Hazardous Operation on it . For my Part I cannot forbear wondring at the Confidence of Ignorant Men , who dare Attack a Humane Body , make Incisions , apply Causticks Actual and Potential ; without a due Knowledge of the Site , Position , Dependance , and other necessary Considerations of the Parts concern'd . The Fatal Consequences of these bold Practices are frequently felt , an Instance or Two of which , are Accidentally shewn , Tab. 13. Fig. 1. Tab. 15. Fig. 2.

I must confess frequent seeing and assisting at Chirurgical Operations may dispose Men to Perform the like again , when Circumstances in all Points shall agree ; but without a Competent , if not Accurate Knowledge of Anatomy , and actual Administration of Dissection , such Persons must be a long Time Spectators , before they can Arrive at a tolerable Pretence to a General Practice : And therefore as I cannot but deplore the Profound and Universal Ignorance which prevails , so I would candidly recommend it to most of the Surgeons in this vast and populous City , to apply themselves with more Industry than they have hitherto done , to so Useful a Part of their Art ; who would soon then be convinc'd this was no Dishonour to themselves , and cease to Reproach others who have spent some of their vacant Hours in these Exercises .

But this is foreign to my purpose , and therefore I shall Address my self to the Business now before me , which is to Present the Reader with a Brief and General Plan of the Animal Oeconomy , as an Introduction to the following Tables .

All the Functions of an Animate Body may be well enough divided into Natural and Animal ; by Natural , I mean all which Terminate in the Body , and Conduce to the preservation of the Individual or Propagation of the Species ; by Animal , I understand such , in which the Soul is concern'd , which in Regard of the Body to which it is United , are Passive or Active ; the First is Sense ; the Latter Voluntary Motion . For the more Orderly Distribution of the Whole , we shall first Treat of the Former , leaving the Animal Functions to succeed ; and here we shall follow the Process of Nature ; beginning with the First Reception of the Aliment in the Mouth , and pursuing it thence thro' its several Stages .

After the Aliment is taken into the Mouth , ( for the more Commodious doing of which , the Dentes Incisorii are often Employ'd ) it here suffers Comminution , and is mixt with Saliva , which is Previous to the Second Preparation , it receives in the Stomach . This Operation is call'd Mastication , and is perform'd by the Lower Jaw , Variously mov'd by its Proper Muscles , and Assisted by the Tongue , Cheeks , and Lips ; which last , still apply the Less divided Parts of the Mass , to the Dentes Molares , for it 's due Comminution ; while all the Neighbouring Muscles in their several Actions , Compress the Parotid , Maxillary , Sublingual Salivary Glands , and those of the Lips , Cheeks , &c. and force them to Discharge their Contents to mix with the Masticated Aliment , now ready for Deglutition .

The Aliment after it has undergone this Alteration , do's not Descend into the Stomach by its own Weight , but is convey'd thither by the joint Action of the Muscles of the Tongue , Os Hyoides , Fauces , and Oesophagus ; all which Conspire in Deglutition , by Raising and Dilating the Gula , and Protruding the Meat into it . The whole Action do's very much resemble the pouring Corn into a Sack , and is done in the Manner I shall just now Describe . The Root of the Tongue being Deprest by means of its Muscular Fibres , its Tip and Sides are applied in a Semicircular Manner , to the Insides of the whole Range of Teeth of the Upper Jaw or Gums , when these happen to be wanting ; and the Whole in this Position is drawn Upwards , by the Musculi Styloglossi and Stylohyoidei , Tab. 14. Fig. 1. Tab. 15. Fig. 1. At the same Time the Fauces are Rais'd by the Musculi Stylopharyngaei , which by their Oblique Position , ( as is Noted App. Fig. 38. ) draw open their Mouth , and Dilate that Cavity . Now Two Thirds at least of the Upper Surface of the Tongue , being applied to the Roof of the Mouth , and drawn as we have now Describ'd , Upwards , and Inwards ; the Epiglottis is Deprest in such Manner , that the Aliment is Protruded over it ( as on a Bridge ) into the Dilated Cavity of the Fauces , and thence by the Contraction of the Musculus Pterygopharyngaeus and Oesophagaeus , App. Fig. 38. it is Deprest into the Gulae , which Helps its Descent into the Stomach , by the Action of its Muscular Fibres .

We must not omit to observe here , That in the Instant the Aliment passes thro' the Isthmus of the Throat , the Gargareon is drawn Upwards and Backwards , by the Musculi Sphaenostaphylini , ( Exprest Append. Fig. 8. ) and the Foramina Narium by this means occluded , while the Epiglottis below covers the Rimula , as was above Noted ; and by this means the Matter in its Passage is hindred from Reverting by the Nose , or Descending into the Wind-Pipe ; The first happens when the Gargareon is wanting , whether by Venerial Exulcerations or otherwise ; or Intumified and Inflamed as in the Small Pox , and cannot yield to this Motion . We may likewise Note , That the Musculus Mylohyoideus ( T. 15. F. 1. ) in its Action does press the Sublingual and Maxillary Glands , and force them to discharge their secreted Liquors , by the Papillae , situated at the Fraenum or Ligament of the Tongue ; and that the Muscles which Contract the Fauces , have the same Effect on the Tonsills and other Glands of that Part ; all which Liquors , discharged from the Mouths of their Excretory Channels , do facilitate the Passage thro' the Gula , and serve to Compose the Stomachick Menstruum ; of which further in the next Paragraph .

After the Aliment , thus alter'd by Comminution and Admistion with the Saliva , is received into the Stomach , we proceed next to consider , how its Second Preparation is perform'd . The great Agent in Digestion is the Stomachick Juice , secreted from the Blood by numerous Glands in this Part , and discharged into its Cavity , in Conjunction with the Spittle . This is that which acts promptly upon the Meat lodg'd in the Capacity of the Stomach , and from the Mixture of these two Juices , is compounded a proper Menstruum , by which the Parts of the Aliment are dissolved , and receive their first Transmutation within the Body . In this Action , which is a Dissolution of the Texture of the Alimentary Mass , the Aerial Parts included in its Pores , now escape from their former Prisons , and being rarified , distend the whole Body of the Stomach ; and this I take to be the true Reason why most Men have less Appetite at some distance of Time , viz. when this Intumescence is made , than immediately after they cease from Eating : From the same Cause arise frequent Eructations , great Inflation from divers Meats , such as Old Pease , Cabbage , Roots , Herbs , and other Vegetables , which very much disturb decay'd debilitated Stomachs . I am apt to suspect the Stomachick Menstruum may excite an Intestine motion of the Particles of the Mass in Digestion ; which yet I do not think fit to call Fermentation , fearing so bold a Term may mislead us into a False Idea of a greater Conflict than really happens .

The Intumescence or Dilatation of the Stomach has two Effects : First to compress the Gall Bladder and Pancreas , and oblige their Ductus Excretorii to spue out their Contents into the Duodenum ; next to retard the Refluent Blood , and by this means dispose the Muscular Fibres of the Ventricle to a Contraction . The Reason of this last Hint will appear by what we have offer'd concerning Muscular Motion , in the Introduction to our Myotomia Reformata .

For the Cause of Hunger which is an observable Phaenomenon belonging to this part , I conceive it to be an Irritation of the Stomach , arising from a copious Quantity of this Menstruum , when it wants Matter to act upon . This conjecture seems more probable , since it is Natural to discharge the Spittle out of the Mouth which comes into it at that Time , rather than suffer it to descend into the Stomach ; and we may perpetually observe a depraved Appetite does follow a Vitiation of the Saliva , as in Scorbutick Habits , Salivations by Mercurial Medicines , and such like Cases .

When the Mass is sufficiently prepar'd and reduced to a Pultaceous Consistence , the Stomach by the help of its Muscular Fibres contracts it self , and expels its Contents thro' the Pylorus into the Duodenum ; where the Digested Mass is mixed with the Bile and Pancreatick Juice , ( forced to discharge it self here as was just now described ) which Volatilize , Subtiliate , and Separate the more Fluid and Fine Parts of the Aliment , from the more Impure and Gross , and here it is that Chylification is first made perfect . Now the Bile abounding with Lixivial Salt , is apt to intangle with the grosser Parts of the Chylaceous Mass , and its Saline Quality not only cleanses the Cavities of the Guts from the Mucus , Excreted by their Glands ( App. Fig. 40. ) ( to smear their Inmost Coat , and defend the Ostia of the Lacteal Vessels from being injured by Extraneous Bodies , which may happen to pass that way ) but Stimulates the Intestines in their Peristaltick Motion .

The Peristaltick or Wormlike Motion of the Guts being thus Accelerated by the Acrimony of the Bile , the Contents of the Intestines are carried on , and the Thinner and more Fluid Parts , fitted for the Pores of the Lacteal Vessels , is absorbed by them , and the Thicker move on more slowly , till by the many Stops they meet with in the Connivent Valves , all the Chyle is at length absorbed , and the Remains being meerly Excrementitious , are only fit to be excluded by Stool .

This Vermicular Motion of the Guts , is perform'd by the Alternate Contraction of their Longitudinal and Transverse Fibres , ( App. Fig. 39.40 . ) which at the same Time convey the Digested Mass thro' the Intestinal Tube , and express the Chyle into the Orifices of the Lacteal Vessels adapted to receive it ; whose Progress from the Intestines , till it is discharged into the Mass of Blood , next presents it self to our Consideration : By the reciprocal Action of these differing Fibres , and the Apposition of the Connivent Valves ( Tab. 39. Fig. 2. ) the Chyle is forced into the Lacteal Vessels , Tab. ib. Fig. 1. ) and hence it is we cannot make any Fluid pass from the Cavity of the Guts into the same Vessels , when the Peristaltick Motion ceases . A farther Use of the Contraction of these Muscular Fibres , is to Accelerate the Chyle in its Progress , till the Lympha derived from the Arteries of the Guts joyn with it , which is done before it leaves the External Surface of the Intestines ; by this Addition the Chyle is diluted and assisted in its Progress towards the Mesenterick Glands ; in the Cells of which it is a Second Time Mixed with a Juice or Lymphatick Liquor there Secreted from the Arteries , and so carried on to the Vasa Lactea secundi Generis . These Vessels resembling Pipes , convey the Chyle from hence , all emptying themselves into the Common Receptacle or Cistern ; the happy Discovery of which , we owe to the Observation of Mons. Pecquet : It is here the Lympha returned from the Inferior Limbs and adjacent Parts , is mixed with the Chyle , ( App. Fig. 11. ) which not only serves to dilute , but promotes its Ascent thro' the Thoracick Duct , ( Fig. ib. ) to the Lest Subclavian Vein , ( Fig. ib. ) where this Channel empties its Contents into the main Current of the Blood . If we consider in this Duct , its several Divisions and Inosculations , ( resembling the Veins of the Testicles ) its numerous Valves looking from below Upwards , its advantageous Situation between the Great Artery and Vertebrae of the Back , together with the Ducts discharging their Refluent Lympha from the Lungs , and the other Neighbouring Parts , we shall find all conduce to demonstrate the utmost Art of Nature , used in furthering the Steep and Perpendicular Ascent of the Chyle ; which Beautiful Order is Represented App. Fig. 11. and cannot but equally Create in us Delight and Admiration .

Having traced this Animal Juice to its Reception into the Blood , with which it is at last Circulated and Assimulated , we shall proceed to the Blood it self , whose Circular Motion , the various Artifices of Nature for adjusting the Proportions and other subordinate Contrivances ; the Manner and Cause of the Contraction of the Heart and Arteries , Respiration , with the whole Theory of the Lympha and Glandular Secretion in the Order of Nature , follow .

The Refluent Blood in the Upper and Lower Trunk of the Vena Cava meeting in the Right Auricle of the Heart , is thence expelled by its Contraction into the Right Ventricle , when the Heart is in its Diastole ; but by its Systole or Contraction , it is thence driven into the Arteria Pulmonaris , from whose Capillary Vessels it passes into the Extremities of the Vena Pulmonaris , and thence returning , is discharged into the Left Auricle and Ventricle of the Heart : From whence it is again by the Systole driven into the Aorta , by whose Branches it is convey'd thro' the whole System of the Body : But when it arrives in the Capillary Arteries , it do's not stop there , but passes into the like Capillary Veins , and from thence into the greater Branches , next into the Trunk of the Vena Cava , and so into the Right Ventricle again . In the mean time the Three Tricuspid Valves in the Right ( Tab. 22. Fig. 6. ) and the two Mitral Valves ( Tab. ead . Fig. 12. ) in the Left Ventricle of the Heart , oppose its return into the Vena Cava and Vena Pulmonaris ; and the Semilunary Valves of the Arteria Pulmonaris ( Tab. ead . Fig. 14. ) and Aorta , ( Tab. ib. Fig. 13. ) prevent its Reflux into the Ventricles . The Structure and Position of which Membranes , are sufficient alone to lead all Observing Men into a compleat Knowledge of its Motion and Progress .

The Circular Motion of the Blood was first Explain'd , and the whole Demonstrated in a Treatise expresly Writ upon that Subject , and Published in the Year 1628. by our Learned and Ingenious Dr. Harvey ; To omit all disputes here how far this was known to Cesalpinus , Columbus , Servetus , or any of the Anatomists or Virtuoso's of the last Age. But the Manner how this Animal Liquor is transmitted from the Arteries to the Veins , has remained hitherto a Secret , and afforded Matter of Controversie . Some pretend this is done by some blind Imperceptible Meatus in the Carnous Parts , and perplex themselves to give Irrational and Chimerical Accounts , which we shall not here lose Time to enumerate or refute . But the late great Improvement of Microscopes has put an end to all these uncertain Conjectures , by discovering to our Naked Eye , that the Veins and Arteries are but one continued inflected Tube , and the Blood passes from one to the other in an uninterrupted Current ; which Unity of the Blood-Vessels by a Parity of Reason , we infer extends to the whole System , and will hardly be questioned by those who consider the Prompt Passage of Mercury , and other injected Liquors from the Arteries to the Veins , or see the Globules of Blood passing these Angustia , and reverting with incredible Rapidity in the Fins of Fishes ; ( App. F. 4 , 5. ) which curious Discovery ought not to be reputed the least Advancement which this Part of Natural History has receiv'd .

The great Engine which sets all this Motion on Foot , is the Heart , ( Tab. 22. Fig. 9. ) by whose repeated Elastick Contraction , the Blood is driven to the remotest Parts thro' the Arterial System , ( App. Fig. 3. ) and forced to continue its Motion back thro' the Venous Channels . This Elastick Force is primarily seated in its own Muscular Fibres , whose Spiral Contortion ( Tab. 22. Fig. 2 , 3. ) is very well described by Dr. Lower in his Book De Corde ; but the Pendulous Position and the Fibres , which compose its Great Arteries , i. e. the Pulmonaris and Aorta , assist very much ; and the Heart taken out of the Body and held up by the Arteries , will continue the least gentle Motion imprest on it for a considerable Time , which Effect can only be ascribed to the Elasticity of the Arterial Trunks by which it is suspended .

The Heart is the immediate Instrument , but what is the Vis Motrix which forces its Fibres to a Contraction , is a far greater Difficulty , and one of the most Abstruse , Inscrutable Mysteries of Nature . It is in this respect our Bodies differ from Artificial Machines ; the Former having in themselves a perpetual Principle of Motion , which the Latter by no Invention of Men can arrive at . In my Opinion the Heart of an Animal bears a great Analogy to the Pendulums of those Artificial Automata , Clocks and Watches , whilst its Motion is perform'd like that of other Muscles , the Blood doing the Office of a Pondus . The Observation of the Curious Mons. Peyer in Parergo Septimo , seems to favour this Opinion ; who tells us , He has with Pleasure seen the Heart renew its Contraction , by blowing into the Thoracick Duct , when the Parts have began to grow stiff after Death . The like Motion of the Heart I have more than once observ'd to be restor'd , by blowing into the Veins of a Dog , and pouring warm Water on it , or applying the Palm of the Hand not long after its Cessation .

Besides the Quantity , doubtless the Quality of the Blood has a Share , since all Distempers which alter the Mass , at the same Time create a Hurry and Disorder in its Motion . To explain the Action of the Blood in this Case , and the Influence it has over the Motion of the Heart , we must consider its Nature , Constituent Parts , and the Alterations it is disposed to receive . This Animal Fluid consists of Two Parts , Serous and Globular . The Distinction of these Parts of the Blood is evident to the Naked Eye , after its Stagnation in any Vessel , but is clearly evinced by the Microscope in its Circulation thro' the Tails and Fins of Fishes , and other Transparent Parts , in the same manner as is Represented Appendix Fig. 4 , 5. where the Globules seem to Swim in the Serum in this state of Mixture . Now the Blood being in this manner a Heterogeneous Liquor , Compos'd of Particles of various Magnitude and Figure , must be subject to an Intestine Motion ; but the great Rapidity of its Current thro' the Arteries , and the Angustiae in the Extremities of the Blood-Vessels , not admitting any Retrograde Motion to be there made , it is deferr'd till it arrives in the Great Veins , where its Progress is retarded , and the Room more spatious , and the Intestine Motion there Commences , which arises to a Greater or Less Height , as the Blood is more or less Charged with Incongruous Parts . The Alteration which the Blood by this means receives , has no inconsiderable Share in the Heart's Contraction ; and tho it be not the prime efficient Cause , yet we cannot deny but that it is Partial and Incitative , as appears in Fevers and several other Distempers , where the whole Mass is Accelerated , and the Pulse more frequent .

Besides all these Causes , the Brain by its Nervous Trunks sent to this Part , which are very Thick and Tense , yet lie very loose , contributes much to this Action . And here we may observe , not only these of the Heart , but the whole System of Nerves which serve the Viscera in the Thorax and Lower Belly , have their Propagines very Numerous and Tense , notwithstanding which , they lie Loose or Free in their Progress from the Brain to their respective Parts ; both which concur in disposing them to Receive and Retain all Impressions from their Extremities : This Faculty beginning to Exert it self even while the Foetus is in Vtero , grows Familiar and Natural , and from this early Habit and Practice of the Infant , they after perform their Duty Sleeping or Waking , without the least Advertence ; but this by the by . And now if what has been Noted , shall be thought sufficient to give ground to Hope Future Enquiries may discover more Adequate Causes of this great Phaenomenon , we have obtained our Desire , and shall leave these Hints to be improv'd by Men of more Industry and Leasure .

Before we leave this Subject , we must not omit to Remark some Observable Artifices of Nature , for the better carrying on the Circulation . The First is the Valves placed in the several Divarications of the Veins , between their Capillar Extremities and Larger Trunks : These are Membranes proceeding from the inner Coat of the Vessels , in the Form of a Crescent or C. which was the Ancient Greek Sigma , and are generally Double , with their Concavity looking towards the Heart , and readily give way to the Current of the Blood thither , as is Represented : ( Tab. 23. F. 7. ) But if by its Weight , or any other Cause , the Blood should Revert , they oppose it , and being Distended , prevent its Return from the Great Trunks of Veins to the Lesser , and at the same time hinder the Superincumbing Blood from pressing on the Inferior ; concerning which consult Tab. 23. Fig. 6.

Another Considerable Artifice in Nature , is the Conveying great Quantities of Refluent Blood from several Parts of the Trunk by particular Channels , instead of discharging it by the next and most immediate Passage into the Neighbouring Current . Dr. Lower has well Observ'd , that the Heart is not placed in the Center of the Body , but inclines to its Upper Part , which Position is necessary to Drive the Blood in its Systole to the Head , with more Force then is required to make it Descend to the Feet , to which its own Weight and Fluidity do's not a little Conduce . Now the Heart being seated so near the Upper Part , as that Two Parts in Three of the whole Fabrick , appear to be below it , there must be a like Inequality of Blood sent to the Inferior Parts , to that which Ascends to the Superior . And this we see Confirm'd by comparing the Diameter of the Blood-Vessels Descending with the Ascending , the Former being much Larger then the Latter . This great Disproportion of Blood in the Upper System to that of the Lower , seems to threaten a great Disturbance in the Animal Order , but is prevented by the Provident Care of the Author of Nature , in the Manner we are now about to Describe .

The Intercostal Arteries App. F. 3. which arise from the Lower System , are accompanied with Veins ( that Return the Blood they Exported ) which do not enter into the next Large Trunk according to the ordinary Process of Nature in other Parts ; but are all United into One Channel ( and sometimes Two ) which Ascends by the Side of the Aorta , and Empties it self into the Descending Trunk of the Vena Cava , there Discharging all its Refluent Blood ; which had it been Inserted into the Ascending Trunk , it must have added so great a Weight , that the Blood could not have past up to the Heart , which it now easily do's . Beside these , the Mammary Veins likewise Empty themselves into the Subclavian , so that all the Blood Arising from the Parietes of the Thorax , the Back and its Muscles , as well as those of the Scapulae , returns again to the Heart , by the Upper Trunk of the Vena Cava , tho' it was sent thither from the Lower Trunk of the Arteria Magna .

Another Contrivance of this Nature is Observable in the Vena Porta , which Receives the Blood from the Stomach , Omentum , Spleen , Pancreas , Guts and Mesentery , sent thither by the Coeliack and Mesenterick Arteries , which large Quantity had it Enter'd into the Vena Cava , immediately below the Liver or Kidneys , its Weight so far beneath the Diaphragm , must have Hindred its Ascent ; wherefore the Vena Porta ( not unlike the Azygos of the Thorax before Noted ) carries up all the Blood by another Channel , and Discharges it into the Extremities of the Vena Cava within the Liver , where it is Diluted and Propell'd by the Refluent Blood from the Splenick Vein , and afterwards assisted in its Ascent , by the Contraction of the Diaphragm .

Here I cannot forbear making a Digression , and presenting my Conjectures of the Use and Office of the Spleen , since it ministers in this Part of the Animal Oeconomy . The Arteria Splenica is not only very large in Proportion to the Magnitude of the Spleen , but has a Remarkable Tortuous Passage to it , ( Tab. 36. F. 1. ) whence we may conceive as the Quantity of Blood sent to the Spleen is very great , so it s Impetus is very much Abated : Next the Communications between the Extremities of its Arteries and Veins are very Large , as appears by the Prompt Exit , which Water pour'd into one Finds by the other , and the Inflation of the Veins which is easily made by Blowing into the Arteries , when the whole Spleen and its Veins become Distended with it . The Lymphe-ducts of the Spleen we have Observ'd , ( Tab. 36. Fig. 1. ) to Arise from the Vesiculae at the Extremities of its Veins , and Discharge their Contents into the Neighbouring Lymphatick Glands , whence it is sent into the Receptacule of the Chyle : Its Nerves are Distributed thro' its whole Substance , and serve to preserve its Tone and Regulate the Separation of its Lympha and Nutritive Juice . But the most exact Scrutiny of Anatomists could never yet Discover any Excretory-duct arising from this Viscus ; and indeed the Patent Communication of its Vessels seems a convincing Proof , that no such Excretory-duct can Exist but must appear very plain . Besides it seems Extravagant and Unbecoming the Wonderful Providence of Nature , to Separate any particular Juice in the Arteries here to be instantly Refunded into the Veins , and we can hardly conceive the Blood can suffer any Alteration , in a Place where the Transit from the one to the other , is so Ample .

After these Considerations Premis'd , if the Problem be Propos'd , What can be the Design of the great Architect of our Bodies , in the Fabrication of so Large and Remarkable a Part , without any Fluid Secreted in it , besides its own Nutritive Juice and Lympha ? I believe our Hypothesis will enable us to give a sufficient Reply to this seeming invincible Difficulty , with which Learned Men have exceedingly perplex'd themselves . I conceive then the Spleen is Design'd by Nature , as a Diverticle to receive a large Proportion of Blood to be Refunded by its Veins into the Porta , and promote the Reflux of the Blood Imported thither from the Stomach , Guts , Pancreas , Mesentery , &c. by whose slow Progress thro' the innumerable Glands of those Parts , it returns Thick and unfit for Motion : And this seems but Necessary that a new Quantity of Blood , charg'd with a Copious Serum , should be Infunded into this Refluent Liquor before it Arrives at the Liver , to dispose it to pass the Extremities of the Vena Cava , and add a fresh Impetus to its Languid Motion caus'd by its Long and Tortutous Progress . This I take to be the Use and Office of the Spleen , and seems to have all the Circumstances the Laws of Mechanism require for this Purpose . The Novelty of which Opinion will ( I hope ) be no Prejudice to its Reception in the Minds of Candid and Impartial Men.

Having thus Represented the Circulation ; the Order of Nature leads us to Respiration , which serves in conveying the Blood from the Right to the Left Ventricle of the Heart , and Impregnates it with Parts proper for its further Elaborations .

Respiration or Breathing is a double Action , i. e. Inspiration or Receiving of Air into the Lungs ; and Expiration or Expelling it again : The whole is done by means of Widening and Straitning the Cavity of the Thorax , in which the Lungs are contain'd .

How the Cavity of the Thorax may be Enlarged and Contracted , we may easily conceive , if we consider the Order of its Bony Parietes , ( Tab. 27 , and 28. ) and observe the Oblique Descending Position of the Ribs from the Vertebrae of the Back , with their Cartilaginous Connection to the Os Pectoris , and the Position and Action of the Diaphragm , as is explained Tab. 52. whence it appears when the Ribs are drawn up , and the Superior Convex Surface of the Diaphragm deprest towards a Plain , the Included Space must necessarily be Enlarged ; and on the contrary very much Straitned when the Ribs are drawn down , and the Upper Surface of the Diaphragm Convex towards the Lungs , as it is Represented in the last mention'd Table .

The Elevation and Depression of the Ribs is perform'd by the Proper and Common Muscles of the Thorax : The First have their Rise and Termination confined to the Parts Composing its Parietes : The Other , notwithstanding their Relation to other Parts , yet chiefly respect This : Of the Common Muscles some are Principal , immediately moving This , together with those Parts from which they are derived : Others are Auxiliary , which by moving the Contiguous Bodies , Contribute to the better performing the Grand Motion : Thus the Elevation of the Shoulder-Blades is required in violent Respirations , without which the Musculi Serrati ( Tab. 20. ) ( which spring from the Scapulae ) ( Tab. 29. V. W. ) could not Act ; hence it happens that Respiration is Interrupted when the Arms are in Action , by reason the Scapulae at that time engage all their Muscles ( especially the Serrati T. 20. ) to render them Stable ; and the Extension of the Vertebrae of the Neck becomes necessary , to the end the Musculi Scaleni ( Tab. 18. B B. ) may Raise the Upper Ribs .

The Proper Muscles of the Thorax are the Intercostales Externi and Interni , ( Tab. 26. Fig. 1. ) the Triangulares , ( Tab. and Fig. ead . ) the Serrati Superiores and Inferiores Postici , Tab. 28.

The Principal Common Muscles , are the Scaleni , ( Tab. 18. ) the Subclavii , Tab. 20. the Serrati Majores & Minores Antici , ( Tab. ead . ) and the Sacrolumbales , ( Tab. 29. )

The Auxiliary Muscles are such as Raise the Scapulae , and draw them Backwards , and those which Extend the whole Spine .

The Cavity of the Thorax being dilated in the manner above mention'd , the Ambient Air necessarily rushes thro' the Aspera Arteria and Bronchia , into the Vesiculae of the Lungs , whereby their whole Substance becomes Distended ; and this we call Inspiration .

In Expiration , the Air contain'd in the Vesiculae of the Lungs , is Excluded ; in this Action the Lungs are not meerly Passive as in the Former , but the Elasticity of the Ligaments of their Bronchia , draw their Small Cartilages over each other , and Conduce to the Expulsion of the Air contain'd in their Vesiculae .

This Alternate Diastole and Systole of the Lungs and Thorax , bears an Analogy to a Pair of Bellows , whose Two Boards being drawn from each other , the Ambient Air necessarily rushes in between them , and Fills the Internal Space enlarg'd by the Deduction of their Sides ; which Air is again Expell'd from thence , by Approaching them towards each other .

The Inducements the Author of Nature had to Frame this Pulmonary Organ , are many ; by this the Aerial Particles pass to the Mass of Blood , which Rarifie , Subtilize and render it fit for those Elaborations it afterwards undergoes : By these the Tenacious Serum of the Blood is Attenuated , and the whole Mass rendred fit for Motion ; the Effects of which are Evident in those Rhumatick Asthmas and other Cases , which Oblige some to leave this Town for a Clearer Air.

The Lungs are the Intermediate Passage between the Two Ventricles of the Heart , whereby the whole Mass of Blood passes thro' their Large Blood-Vessels in an equal Rapidity and Quantity , with that of all other Parts of the Body besides , and do by this means discharge the Blood of a great Quantity of its Serum , by Halitus in Expiration ; wherefore the Accurate Dr. Tyson Reckons them among the Number of Glands .

This Alternate Action in which Respiration consists , is Necessary , to the End the Blood may pass the Lungs , whose Vesiculae , if they were constantly Distended by the Inspired Air , the Extremities of the Pulmonick Blood-Vessels would be Comprest ; and on the contrary , if these Vesiculae were Collaps'd ( as after Expiration ) their Blood-Vessels would be consequently Corrugated ; but by this Vicissitude they become Permeable , and the Blood easily passes their Extremities .

We have Traced the Aliment from its First Reception till it is Elaborated into Blood , and pursued in its Motion and Circulation thro' its several Channels . We ought next to take a View of the several Liquors or Fluids separated from it in its Tour. All Animal Juices except the Chyle are separated from the Arterial Blood , which common Material in its Percolation in the Brain and Nerves , yield the Contents of their Fibres ; in the Glands of the Mouth and Throat , the Saliva ; in the Mammae , the Milk ; in the Kidneys , the Urine ; in the Testes , Sperm ; ( not to name the Sweat , Mucilage of the Joints , &c. ) and thro' the Universal Body , a Copious Quantity of Lympha ; which is not applied to any distinct Use in the Animal Oeconomy , but is all discharg'd into the Great Cystern or Receptacle of the Chyle and Subclavian Vein , and so Refunded into the Refluent Blood .