ANATOMY. 



suits, of their moving on each other with 

 Freedom and facility. Its deposition under 

 the integuments gives a roundness and 

 convexity to the surface, on which the 

 beauty of the human form principally de- 

 pends. Indeed, its accumulation in par- 

 ticular situations immediately influences 

 the outline of the part; as in the orbit, 

 the cheek, and the buttocks. The effects 

 of its loss is most disagreeably manifested 

 in the lank cheek and hollow eye of an 

 emaciated patient. 



It has been supposed that the fat ab- 

 sorbed under certain circumstances is 

 applied to the nutrition of the body ; as 

 in hybernating animals. 



JMembranes. In the foregoing observa- 

 tions on cellular substance, we have stated 

 that membranes are formed by a conden- 

 sation of that substance. They consist of 

 thin sheets of compacted and close cellu- 

 lar texture. This is proved by long ma- 

 ceration in water. The fluid gradually 

 penetrates the interstices, and resolves 

 the membrane into a loose and flocculent 

 substance. They are found in every va- 

 riety of density and softness. 



A grand use of membranes is, to line 

 what anatomists call the circumscribed ca- 

 vities of the body. These are hollow 

 spaces, containing the different viscera, 

 and in every instance complete!}' and ac- 

 curately filled by such viscera; so that 

 the term cavity, when used by anato- 

 mists, does not, as in common language, 

 denote a void or empty space. 



Membranes have a smooth internal po- 

 lished surface, turned towards the con- 

 tained viscera. This is constantly moist- 

 ened by a lubricating fluid exhaled by the 

 minute arteries of the part, and bestows 

 on the surface of the membrane the 

 greatest softness and smoothness. Hence 

 the motions of the viscera are performed 

 with perfect facility, and they are pre- 

 vented from adhering to each other, or to 

 the sides of the containing cavity. The ex- 

 tent of such cavities is bounded and de- 

 fined by the lining membranes, and hence 

 arises the epithet circumscribed. To in- 

 crease the facility of motion, the surface 

 of the contained viscera is covered by a 

 continuation of the same membrane, and 

 always therefore possesses the same 

 smoothness and polish with the sides of 

 the cavity. The membrane lining a cir- 

 cumscribed cavity is a complete and en- 

 tire sac, which is reflected over all the vis- 

 cera contained in the cavity. In the carcase 

 of an animal just slaughtered, the lubricat- 

 ing secretion flies off in the form of a fine 

 vapour when the cavity of the belly or 



VOL. I. 



chest is laid open. It is nothing mor.e 

 than an increase of this natural secretion, 

 combined perhaps with a deficient ab- 

 sorption, that gives rise to dropsies of the 

 different cavities. 



The opposite or external surface of the 

 membrane is rough and cellular; and ad- 

 heres to the various parts which form the 

 sides of the cavity. 



Another use of membranes is, to form 

 blood-vessels, or tubes for conveying the 

 nutritious fluid to all parts of the body. 

 The bore or hollow of the tube is per- 

 factly smooth and polished, so that the 

 blood experiences no obstruction in its 

 course ; and the external surface is rough, 

 to connect it with the surrounding parts. 

 In a similar manner are formed the sto- 

 mach and intestines, which receive the 

 food ; the urinary bladder, which holds 

 the urine, &c. 



It must be obvious, that for all the pur- 

 poses which we have enumerated, whe- 

 ther for lining circumscribed" cavities, for 

 conveying the blood, for receiving the 

 food, or holding any other liquors, it is 

 essentially necessary that membranes 

 should be impermeable to fluids in the 

 living state. 



OSTEOLOGY. 



The bones are the most solid parts of 

 the body. They are composed of a vas- 

 cular substance, not differing materially 

 in structure from that of the rest of the 

 body, except that there is deposited in 

 its insterstices an earthy matter, which 

 gives to the whole mass rigidity, strength, 

 and a permanent figure. The nutrient 

 vessels of arteries, membranes, and liga- 

 ments, occasionally deposit lime, and 

 cause the ossification of those parts. 



The account of the original formation 

 of the bones in the foetus, is technically 

 termed osteogeny. The parts of the young 

 fostus, which are afterwards to become 

 bones, are at first cartilaginous ; and their 

 substance is rendered white and firm, in 

 proportion to the quantity of lime depo- 

 sited in it. The quantity at the time of 

 birth is only sufficient to give firmness to 

 the whole mass, not to prevent its flexibi- 

 lity. 



The extremities of all the long bones 

 consist of large portions of cartilage, and 

 these by degrees become bony. The for- 

 mation of bone begins in the centre of 

 the cartilage, and gradually extends from 

 thence to the remote parts, so that the 

 separate piece of bone, formed at the ex- 

 tremity, remains till near the time of pu- 

 berty, conjoined to the body of the bone 



7 



