10-12, 15.
[1011] Ibid. _c._
[1012] PLATE IX. FIG. 7, 11, 12, 15, 19. _g´._ The _Collare_
of _Hymenoptera_ and _Diptera_ has usually been regarded as
representing the _Prothorax_ of _Coleoptera_, _Orthoptera_, &c.
But this difference obtains between them--the latter evidently
belongs to the _Manitrunk_, and its muscles do not appertain at
all to the _Alitrunk_; whereas the _Collare_ as evidently is a
part of the latter, its muscles belong to it, and its functions in
assisting in flight are important. These reasons, and others we
shall state hereafter, induced us long ago to consider this part
as not representing the _Prothorax_; and they seem to have induced
M. Chabrier almost to adopt a similar opinion. _Sur le Vol des
Insectes._ _Ann. du Mus._ 3eme Ann. 414. et 4eme Ann. 54--.
[1013] PLATE XXII. FIG. 8, 11. _h´._
[1014] Ibid. FIG. 8. PLATE VIII. FIG. 3, 12, 14, 16. IX. FIG. 1, 7,
8, 10-12, 15, 19, 21. _i´._
[1015] PLATE VIII. FIG. 14, 20. IX. FIG. 11, 12. and XXII. FIG. 8.
_b´´._
[1016] PLATE X. FIG. 1.; and XXVIII. FIG. 1-8, 10.
[1017] PLATE XXVIII. FIG. 3-5. _b´´´._
[1018] PLATE X. FIG. 1. _c´´´._
[1019] PLATE XXVIII. FIG. 6-8. _d´´´._
[1020] PLATE XXIII. FIG. 6. _e´´´._
[1021] PLATE XXVIII. FIG. 2. _a´´´._
[1022] Ibid. FIG. 19. and PLATE X. FIG. 2.
[1023] The upper organs of flight of many of the _homopterous_
section of the _Hemiptera_ seem altogether membranous, and may almost
be included under the term _Alæ Superiores_.
[1024] PLATE X. FIG. 3.
[1025] Ibid. _f´´´._
[1026] PLATE X. FIG. 3. _g´´´._
[1027] Ibid. FIG. 5-9, 11-15. and PLATE XXVIII. FIG. 18.
[1028] Ibid. _h´´´._
[1029] N.B. In the Plate the _Costal Area_ is _red_, the
_Intermediate white_, and the _Anal yellow_. When the _Hemelytra_
are considered as divided into _Areas_, the _Membrana_ might be
denominated the _Apical Area_.
[1030] PLATE X. FIG. 2, 3, _b^.._
[1031] Ibid. _c^.._
[1032] PLATE X. FIG. 2, 3. _d^.._
[1033] Ibid. FIG. 7-15. _e^.._
[1034] Ibid. _f^.._
[1035] Ibid. _g^.._
[1036] Ibid. _h^.._
[1037] Chabrier _Sur le Vol des Insectes_, _Ann. du Mus._ 3eme ann.
428, 4eme ann. 325--. 3d Cahier 78.
[1038] _Linn. Trans._ i. _t._ xiii. _f._ 2. 3. _d._
[1039] PLATE X. FIG. 5-15. _i^.._
[1040] Ibid. _a*._
[1041] Ibid. FIG. 6. _k^.._
[1042] Ibid. _l^.._
[1043] Ibid. FIG. 5, 6, 13. _b*._
[1044] Ibid. FIG. 5-15. _m^.._
[1045] Ibid. FIG. 5, 6, 13. _c*._
[1046] PLATE X. FIG. 5-15. _n^.._
[1047] Ibid. _o^.._
[1048] Ibid. FIG. 14. _p^.._
[1049] Ibid. FIG. 11. _m´´´._
[1050] Ibid. FIG. 14, 15. _n´´´._
[1051] PLATE IX. FIG. 5, 11. _g´´._
[1052] PLATES VIII. IX. XXVIII. _k´._
[1053] Ibid. _l´._
[1054] PLATE IX. FIG. 7. _m´._
[1055] PLATE VIII. FIG. 4, 13, 17.; and IX. FIG. 3, 8, 12. _d._
[1056] Ibid. _n´._
[1057] PLATES VIII. IX. _o´._
[1058] PLATE VIII. FIG. 4, 8, 13, 17. _p´._
[1059] PLATE XXII. FIG. 6. _q´._
[1060] PLATE XVI. FIG. 4-6. _r´._
[1061] PLATE VIII. FIG. 3, 12.; and IX. FIG. 1, 7, 10, 11, 12, 15. _c._
[1062] PLATE XXII. FIG. 9, 11. _s´._
[1063] PLATE VIII. FIG. 3, 12, 20. and IX. FIG. 7, 10-12, 15, 20. _t´._
[1064] Ibid. _u._
[1065] PLATES VIII. IX. XXVIII. _v´._
[1066] PLATES VIII. and IX. _w´._
[1067] PLATE X. FIG. 4, 10.
[1068] PLATE X. FIG. 4. _o´´´._
[1069] _Linn. Trans._ i. _t._ xiii. _f._ 1. _b._ 3. _a._
[1070] Kirby _Mon. Ap. Angl._ i. _t._ xiii. _f._ 19.
[1071] De Geer ii. _t._ ix. _f._ 9. _d._
[1072] Ibid. vi. _t._ ii. _f._ 23. _a a._
[1073] PLATE IX. FIG. 19. _p´´´._
[1074] Ibid. FIG. 7. and PLATE XXII. FIG. 14. _k´´._
[1075] PLATE XXII. FIG. 10, 11. _x´._
[1076] Ibid. FIG. 9-11. _l´´._
[1077] PLATES VIII. and IX. _f._
[1078] Ibid. _y´._
[1079] Ibid. _z´._
[1080] PLATE XXIX. FIG. 15. _m´´._
[1081] PLATES VIII. IX. _a_†.
[1082] PLATE XXVII. FIG. 50.
[1083] PLATE XXII. FIG. 3. _b_†.
[1084] PLATE VIII. FIG. 18; and XXII. FIG. 13. _c_†.
[1085] PLATE XIV. FIG. 5-8.
[1086] PLATE VIII. FIG. 2, 4, 11, 13, &c. _o´´._
[1087] Ibid. FIG. 18. _q´´´._
[1088] PLATE XIV. FIG. 6-8; and XXVII. FIG. 12. _p´´._
[1089] Ibid. _q´´._
[1090] PLATE XIV. FIG. 5-8; and XXVII. FIG. 6-8. _r´´._
[1091] PLATE XXVII. FIG. 7, 8, 15. _r´´´._
[1092] PLATE XIV. FIG. 5-8. _s´´._
[1093] PLATE XXVII. FIG. 21. _s´´´._
[1094] Ibid. FIG. 9, 10, 16, 17. _t´´´._
[1095] Ibid. FIG. 34-36. _u´´´._
[1096] PLATE XIV. FIG. 6; and XXVII. FIG. 29-36. _v´´´._
[1097] PLATE XIV. FIG. 5-8; and XXVII. FIG. 44, 45, 62, 63. _t´´._
[1098] PLATE XXVII. FIG. 25, 26, 41. _w´´´._
[1099] PLATE XXVII. FIG. 25, 26. _x´´´._
[1100] PLATE XXVI. FIG. 47, 48; and XXVII. FIG. 43. _r^.._
[1101] Ibid. _s^.._
[1102] PLATE XXVI. FIG. 47, 48. _d*._
[1103] PLATE XXVII. FIG. 37-57. _e*._
[1104] Ibid. FIG. 56, 57. _f*._
[1105] Ibid. FIG. 56. _a_ ψ.
[1106] Ibid. FIG. 59. _y´´´._
[1107] PLATE XV. FIG. 9; and XXVII. FIG. 35, 59-61. _t^.._
[1108] PLATE VIII. FIG. 5, 6, 9, 15, 18, 19.
[1109] Ibid. FIG. 5, 15. _A._
[1110] Ibid. _A´._
[1111] Ibid. FIG. 5, 9. _B´._
[1112] Ibid. FIG. 5, 9, 15. _A´´._
[1113] PLATE VIII. FIG. 6, 9, 15. _B._
[1114] The scientific reader must recollect that these terms
are employed, not because these parts are thought to be true
representatives of the _Epigastrium_ and _Hypochondria_ of vertebrate
animals, but merely on account of some analogy between them.
[1115] PLATE VIII. FIG. 6. _C´._
[1116] Ibid. _D´._
[1117] Ibid. _B´´._
[1118] Ibid. FIG. 18, 19. _C´´._
[1119] Ibid. FIG. 6, 9, 15. _E´._
[1120] PLATE VIII. FIG. 9. _D´._
[1121] PLATE IX. FIG. 17, 18. _C._
[1122] Ibid. FIG. 13. _F´._
[1123] Ibid. _G´._
[1124] Ibid. FIG. 17. _H´._
[1125] Ibid. FIG. 18. _I´._
[1126] PLATE XV. FIG. 12. _D._
[1127] PLATE VIII. FIG. 5, 15. _K´._
[1128] Ibid. FIG. 6, 15, 18. _L´._
[1129] PLATE XV. FIG. 18-22; and XVI. FIG. 1-3.
[1130] PLATE XV. FIG. 18. _E´._
[1131] PLATE XV. FIG. 22; and XVI. FIG. 2, 3.
[1132] Ibid. FIG. 20, 21; and XVI. FIG. 1. _F´´._
[1133] PLATE XV. FIG. 20. _G´´._
[1134] Ibid. FIG. 20, 21; and XVI. FIG. 1. _II´´._
[1135] Kirby _Mon. Ap. Angl._ i. _t._ xii. _Apis_ **. e. 1. _neut.
f._ 23-25; and _t._ xiii. _f._ 27, 28.
[1136] _Ibid._ _t._ xiii. _f._ 30, 31.
[1137] _Ibid._ _a._
[1138] PLATE XV. FIG. 12. _L´´._
[1139] PLATE XV. FIG. 14. _M´´._
[1140] Ibid. FIG. 17. _N´´._
[1141] Ibid. FIG. 15. _O´´._
[1142] Ibid. FIG. 13. _P´´._
[1143] Ibid. FIG. 23. _Q´´._
[1144] De Geer iii. _t._ xxii. _f._ 10. _a a._
[1145] Ibid. _t._ xxiv. _f._ 2. _c_; and _f._ 11.
[1146] PLATE XV. FIG. 16. _R´´._
[1147] Ibid. _S´´._
[1148] Ibid. FIG. 10; and PLATE XXIII. FIG. 16, 17. _T^*´´._
[1149] Ibid. FIG. 12. _B´´´._ 15.
[1150] De Geer _ubi supr._ _t._ iii. _f._ 5, 20, 21. _c._
LETTER XXXIV.
EXTERNAL ANATOMY OF INSECTS.
THE HEAD, AND ITS PARTS.
Before I confine my observations to the _head_ of insects, which I
propose to consider separately in the present letter, I must premise
a few words upon their _body_ in general, or rather its _crust_, or
external integument. In this we may notice its _substance_, general
_form_, _sculpture_, _pubescence_, and _composition_.
i. I have already noticed the _substance_ of this integument in
the preparatory states of insects[1151]; I shall not, therefore,
here repeat what I then said, but restrict myself chiefly to the
consideration of it as it is found in their _last_ state, in which
it is usually firmer than in their previous stages of existence. In
this respect, however, it varies much in the different Orders, and
even in the different genera of the same Order. In some Coleopterous
insects, for instance, it is very hard, and difficult to perforate;
while in others it is soft, flexible, and a pin easily passes through
it[1152]. And in general, from a substance in hardness resembling
horn or shell, it passes through the intermediate degrees of that of
leather and parchment, almost to a thin membrane. Yet in all cases
there is enough of rigidity and hardness to answer the principal uses
of a skeleton--to afford, namely, a sufficient point of attachment
for the muscles, and to support and defend the interior organization;
so that the play and action of the vital and secretory systems may
not be interrupted or impeded.
With respect to the principles which enter into the composition
of this integument, very little seems to be known at present; but
few insects having been submitted to a chemical analysis. The
blister-beetle (_Cantharis vesicatoria_), from its importance in
medicine, has, however, been more than once analysed; and though the
products have not been very precisely stated, yet we find amongst
them phosphate of lime, albumen, and some other usual components
of the substance of vertebrate animals[1153]. But which of these
products belong to the integument, and which to its contents, cannot
be ascertained, without a separate process for each; which would
not, I conceive, be very feasible. The substance, however, of the
integument of insects, though we know not its precise contents,
which probably vary in different genera, &c., appears not to be
exactly of the nature of any of those substances after which it
has usually been denominated: it is not properly analogous either
to real _horn_, _shell_, _skin_, or _leather_, &c. This seems to
result from the following circumstance:--Most of the excretions of
vertebrate animals, as horn, skin (at least when tanned), feathers,
wool, hair, &c. when exposed to the action of fire liquify, more or
less, before they incinerate; emitting at the same time a peculiar
and disagreeable scent: but upon applying this test to the parts of
insects of the different Orders, I found, in every instance, that
incineration took place without liquefaction, and was unaccompanied
by that peculiar scent which distinguishes the others. Even the
_claws_, which to the eye appear, as to their substance, exactly
like those of _Mammalia_, birds, &c. burn without melting, and
retain their form after red heat. That the insect integument is
not _calcareous_ like that of the _Crustacea_, and the shells of
_Molluscæ_, you may easily satisfy yourself, by immersing them in
an acid test. I made this experiment upon portions of insects of
several of the Orders, in an equal mixture of muriatic acid and
water, and the result was, not only that all hexapods, but octopods,
_Arachnida_, and even _Scolopendridæ_, upon immersion only emitted
a few air-bubbles; while, when the other myriapods, _Polydesmus_,
_Iulus_, _Glomeris_, &c. and the _Oniscidæ_, were immersed, a
violent effervescence took place; proving the different nature of
their substance. It is remarkable that the two great branches of
the _Myriapods_, the _Scolopendridæ_ and _Iulidæ_ (_Chilopoda_ and
_Chilognatha_ Latr.), should in this respect be so differently
circumstanced--the latter having a calcareous integument, and the
former not.--A further difference distinguishes these two tribes:
_old_ specimens of the _Iulidæ_ usually lose their colour and turn
white, like _Oniscidæ_; while those of the _Scolopendridæ_ retain it.
ii. The _form_ of insects is so variable, that it can be reduced to
no other general rules--than that, for the most part, the length
exceeds the breadth, and the breadth the depth, and that the upper
surface is usually convex. But to these rules there are numerous
exceptions. Thus many _Tetyræ_ F. (_Scutellera_ Latr.), a kind of
bug, are as broad as they are long[1154]; in the genus _Gonyleptes_
K.[1155] amongst the _Aptera_, and _Epeira cancriformis_, a
crab-shaped spider, the breadth exceeds the length; in _Cynips_, and
several other _Hymenoptera_, in _Acrida_ K.[1156] (_Locusta_ F.), and
other Orthopterous insects, the depth exceeds the breadth; and in
that singular beetle, _Eurychora_; the cockroach (_Blatta_), &c. the
upper surface is flat.
iii. The _sculpture_ of the integument of insects is often very
remarkable; but as this will call for attention hereafter, I shall
only here observe in general, that ornament and variety seem not to
be the sole object of those elevations and depressions which form so
prominent a feature of many of the animals in question; for by means
of these, many important purposes, that at first sight do not strike
the observer, may be served: such as giving firmness to the crust
in those places where it is most wanted; diminishing its powers of
resistance in others, so that it may yield somewhat to the action of
the muscles; increasing or deducting from the weight of the body,
so as to produce a proper equipoise during its motions, whether on
the earth, in the air, or in the water. The depressions of the outer
surface of the crust, in many instances, produce an elevation of
it in the interior, and so afford a useful point of attachment to
certain muscles. This observation seems more especially applicable
to those excavations that are common to particular tribes or genera:
thus the dorsal longitudinal channel to be met with on the prothorax
of most of the _Carabi_ of Linné on the inside of the crust have a
corresponding ridge. In _Locusta Dux_, also, (a Brazil locust,) the
same part has _four_ transverse channels, corresponding with which
on the inside are as many _septa_, or ridges, to which muscles are
attached; and those larger impressed puncta denominated _puncta
ordinaria_, which distinguish the same part in _Geotrupes_ and many
of the _Scarabæidæ_, within are elevated, so as to form a kind of
ginglymous articulation with the base of the anterior coxæ. The
other impressed puncta so often to be seen on the different parts
of various insects, which sometimes so intirely cover the surface
that scarcely any interval is discoverable between them, though in
many cases they appear to be mere impressions that attenuate but
do not perforate the crust--yet in others, perhaps equally or more
numerous, they are real _pores_, which pass through the integument.
If, for instance, you take the thoracic shield of the cockchafer
(_Melolontha vulgaris_), and after removing the muscle &c., hold it
against the light, with the inner side towards the eye, you will see
the light through every puncture: or take the elytra of _Geotrupes
stercorarius_, or any common beetle in which these organs have
punctate striæ, and examine them under a lens on the inside, and you
will see distinctly that the punctures pass through the elytrum, and
the membrane that lines it[1157]. It is not improbable that in the
case last mentioned these pores may be of use, as the spiracles are
usually closely covered by the elytra, for the better transmission of
the air to those respiratory organs. Whether the pores in the other
parts of the body are for transpiration, is more than I shall venture
to affirm; but as insects sometimes perspire, at least this has been
ascertained with respect to the hive-bee[1158], this must be by the
means of some pores.
iv. The integument of insects is often clothed, either partially or
generally, with _pubescence_, or hairs of various kinds--a circumstance
which seems to have more than one object. In _Parnus_, _Heterocerus_,
_Gerris_, _Argyroneta aquatica_, and some other aquatic insects, the
end in view seems to be to keep the water from wetting the crust; and
in this case the covering of hairs is dense, silky, and decumbent.
Another object is preventing friction from being injurious: thus
humble-bees, that from their mode of nidification[1159], are usually
more particularly exposed to it, are well clothed with hair; and in
those articulations of insects where much friction takes place, we may
often observe a dense fringe or coating of the same substance. This
you may see in the common stag-beetle (_Lucanus Cervus_), where the
thorax receives the head; and very remarkably at the same point in the
Hercules-beetle (_Dynastes Hercules_ MacLeay): but besides these uses,
there is probably one more universal, which will apply as well to those
thinly scattered bristles and hairs, here and there one, to be noticed
in many insects: but concerning this I can only throw out a conjecture,
as I do not recollect ever to have seen any experiments with regard to
this use of animal hairs. But may they not act as conductors, either to
introduce some invisible fluid into the body in a positive state, or to
convey it out, when received by other means, in a negative state? Every
one knows that the fur of a cat has electric properties, and there may
be an important general use of this kind attached to the fur and hairs
of animals[1160]. But, as I said, I give this as a mere conjecture;
and only wish it may excite your attention to the subject, and put in
exercise your natural tact for experiment.
M. Cuvier regards the hairs of insects as merely a continuation of
the epidermis, with which they fall when the animal changes its
skin[1161]; but this will apply only to the hairs of larvæ: for the
hairs of perfect insects in many cases are implanted in a pore, and
pass through epidermis or crust to the membrane that lines it, in
which they terminate.
v. We are now to consider the _composition_ of the integument; under
which term I would include the different layers of which it consists,
and its articulation.
1. With respect to the _first_ of these circumstances, the
_layers_ of which the integument consists, it seems to exhibit
some, although not an exact, analogy with the _skin_, rather than
the _skeleton_, of the vertebrate animals[1162]. In these last, the
skin is stated to consist of _four_ layers. Of these the exterior
one is the _epidermis_, or scarf-skin: under this is the _rete
mucosum_, or mucous tissue, which gives its colour to the skin; next
follows the _papillary tissue_ formed by the extremities of the
nerves, and in which the sense of _touch_ principally resides; the
last and innermost layer is the _skin proper_, or leather, called
_Dermis_, _Derma_, or _Corium_[1163]. _Two_ of these layers M.
Cuvier assigns to insects. They have, he observes, in every state,
a true _epidermis_[1164]; and in their state of larva he finds
that the infinite variety of colours that so adorn many of them is
produced by a mucous substance observable between the epidermis
and the muscles[1165]: this seems analogous to the _rete mucosum_.
To this, dried and mixed with their horny substance, he attributes
also the colours of the perfect insect: "for," says he, "when the
_Lepidoptera_ are in the chrysalis, the little coloured scales
which are to ornament their wings, are then in a state of mucosity
similar to that which is found under the skin of the caterpillar.
The colours of the _Arachnida_," he goes on, "are also due to this
mucosity: it is discoverable under the skin, and has the appearance
of minute glandular points of which the shades vary considerably.
But in the _Coleoptera_, and many other Orders, the colours of the
skin are mixed in its horny tissue, nearly as those of the _Testacea_
are in their calcareous shells"[1166]. In the perfect insects,
therefore, in most cases, we may consider the _epidermis_ and _rete
mucosum_ as together forming the exterior and coloured integument of
insects--that part which in the table, since it is not properly an
_epidermis_, I have distinguished by the name of _Exoderma_.
The learned author just quoted has observed nothing under the skin
of white-blooded animals that he regards as analogous to _nervous
papillæ_[1167]. In some parts of insects, as in the lamellæ of the
antennæ of the _Petalocera_, and the extremities of the joints,
especially the last, of many palpi, there is however an appearance
of them; and it seems reasonable to suppose that where the sense
of _touch_ resides, there must, even in insects, be something of a
_papillary tissue_.
With regard to the innermost integument of the vertebrate animals,--the
_leather_, or real skin,--this learned comparative anatomist finds
nothing analogous to it in the integuments of insects[1168]; but as he
does not notice it, he appears to have overlooked the substance that
lines the outer crust, or _exoderma_, in the _Coleoptera_ and most
other orders. This is not always easily detected; but it may generally
be discovered by breaking, or rather tearing (not cutting), after
having cleared away the muscles, any part of the body of an insect.
It is always very visible on the under side of _elytra_[1169], but is
not discoverable in _tegmina_. It appears to consist, in many cases,
of several layers of a whitish membrane, and generally breaks into
fibres. In some elytra of the larger _Dynastidæ_, towards the sides
the exterior layer is separated from the rest by a kind of cellular
substance. The fibrous structure of this inner skin (which I call the
_Esoderma_) seems to give it some affinity to the skin of vertebrate
animals[1170]. In many parts of the body, however, it appears to be
merely a thin pellicle. A medical friend, to whom I showed specimens of
it, thinks it a kind of cellular membrane.
2. A few words are next necessary with regard to the _articulation_
of the integument, or the mode by which the several pieces of which
it and its members consist, are united to each other. In some, as
in several of the parts of the head, the occiput, vertex, temples,
cheeks, &c.--the line of distinction is merely imaginary; in others
an impressed line separates a part from its neighbours, as is the
case with the _nose_ in _Vespa_, &c. the head in the _Arachnida_. But
in the majority of instances the parts are separated by a suture, or
form a real joint. The kinds of articulation observed by anatomists
in vertebrate animals do not all occur in insects, and they seem to
have some peculiar to themselves. Thus, for instance, they have no
proper _suture_; for though they exhibit the appearance both of the
_harmonic_ and _squamose_ (_ecailleuse_ Cuv.) sutures[1171], yet
these parts being all limited by the _esoderma_, or skin, above
noticed as lining the integument, and all admitting a degree of
motion more or less intense, rather afford examples, as the case
may be, of other kinds of articulation[1172]. Again, they have no
proper _Enarthrosis_, or ball and socket; though the anterior coxæ
of the Capricorn-beetles (_Cerambyx_ L.) approach very near to this
kind of articulation, as will be shown more fully in another place.
The inosculating segments or rings, which distinguish the abdomen,
and sometimes other parts of insects, are an example of a kind of
articulation not to be met with in the _Vertebrata_. The ginglymous
articulation, in which the prominences of the ends of two joints
are mutually received by their cavities, and which admits only of
flexion and extension, often prevails in the limbs, &c. of insects;
but in many cases the joints are merely suspended to each other by a
ligament or membrane; and, in fact, the integument of insects, with
regard to its articulation, even where the joints ginglymate, may
be said in general to consist of pieces connected by the internal
ligament, membrane, or skin that lines it; for even in the legs,
where the ginglymous articulation is sometimes very remarkable and
complex, as will be shown to you hereafter, the joints are also
connected by this substance, as you may see if you examine the legs
of any Coleopterous insect.
The _number_ of articulations or pieces that form the integument and
its members in these animals, varies greatly in different tribes,
genera, &c. Thus, in the common louse (_Pediculus humanus_) they
scarcely reach fifty, while in some cockroaches (_Blatta_) they
amount to more than eight times that number.
Having premised these observations on the external anatomy of the
body in general, in the remainder of the present letter I shall
confine myself to the consideration of the _head_ and its _parts_.
I. The _Head_ of insects, as the principal seat of the organs of
sensation, must be regarded in them, as well as in the vertebrate
animals, as the _governing_ part of the body. It may be considered with
respect to its _substance_, _figure_, _composition_, _superficies_,
_proportion_, _direction_, _articulation_ with the _trunk_,
_motions_--and more particularly as to its _parts_ and _appendages_.