Chapter XIX: Part 19

In modern times the most celebrated armlets are those which form part of the regalia of the Persian kings and formerly belonged to the Mogul emperors of India, being part of the spoil carried to Persia from Delhi by Nadir Shah in 1739. These ornaments are of dazzling splendour, and the jewels in them are of such large size and immense value that the pair have been reckoned to be worth a million sterling. The principal stone of the right armlet is famous in the East under the name of the _Darya-i-nur_, "sea (or river) of light." It weighs 186 carats, and is considered the diamond of finest lustre in the world. The principal jewel of the left armlet, although of somewhat inferior size (146 carats) and value, is renowned as the _Taj-e-mah_, "crown of the moon." The imperial armlets, generally set with jewels, may also be observed in most of the portraits of the Indian emperors.

Bracelets have at all times been much in use among barbaric nations, and the women frequently wear several on the same arm. The finer kinds are of mother-of-pearl, fine gold or silver; others of less value are made of plated steel, horn, brass, copper, beads, &c. Chinese bracelets are sometimes cut out of single pieces of jade.

This species of personal ornament has been exceedingly common in Europe from prehistoric times onward. The bracelets of the Bronze Age were of either gold or bronze, silver being then unknown. In shape they were oval and penannular with expanding or trumpet-shaped ends, having an opening between them of about half an inch to enable them to be easily slipped over the wrist. Those of gold were generally plain, hammered rods, bent to the requisite shape, but those of bronze were often chased with decorative designs. Some forms of spiral armlets of bronze, peculiar to Germany and Scandinavia, covered the whole fore-arm, and were doubtless intended as much for defence against a sword-stroke as for ornament. Among the nations of classical antiquity, bracelets were worn by both sexes of the Etruscans; by women only among the Greeks, except in orientalized communities. Among the Romans they were worn by women only as a rule, but they are also recorded to have been used during the empire by _nouveaux riches_, and by some of the emperors. It should also be mentioned that bracelets were conferred as a military decoration in the field.

FIG. 2.--Greek Bracelet, Hermitage.]

The bracelets of the Greeks are of two leading types, both of which were also familiar to the Assyrians. The one class were in the form of coiled spirals, usually in the form of snakes, a term which Pollux gives as a synonym for bracelet. The other class were stiff penannular hoops, capable of being slightly opened. In such examples the terminals are finely finished as rams' heads, lions' heads, or (as in the accompanying figure from a bracelet found at Kuloba) as enamelled sphinxes. In late Etruscan art the bracelet may be formed of consecutive panels, as often in modern jewelry.

FIG. 3.--Etruscan Bracelet, Louvre.]

The spiral forms were common in the Iron Age of northern Europe, while silver bracelets of great elegance, formed of plaited and intertwisted strands of silver wire, and plain penannular hoops, round or lozenge-shaped in section and tapering to the extremities, became common towards the close of the pagan period. The late Celtic period in Britain was characterized by serpent-shaped bracelets and massive armlets, with projecting ornaments of solid bronze and perforations filled with enamel. In the middle ages bracelets were much less commonly used in Europe, but the custom has continued, to prevail among Eastern nations to the present time, and many of the types that were common in Europe in prehistoric times are still worn in central Asia.

A treatise, _De Armillis Veterum_, by Thomas Bartholinus, was
published at Amsterdam in 1676.

BRACHIOPODA, an important and well-defined but extremely isolated class of invertebrates. The group may be defined as follows: Sessile solitary _Coelomata_ with bivalved shells usually of unequal size and arranged dorso-ventrally. The head is produced into ciliated arms bearing tentacles. They reproduce sexually, and with doubtful exceptions are of separate sexes.

The name Brachiopod ([Greek: brachion], an arm, and [Greek: pous, podos], a foot) was proposed for the class by F. Cuvier in 1805, and by A.M.C. Dumeril in 1809, and has since been very extensively adopted. The division of the group into _Ecardines_ (_Inarticulata_), with no hinge to the shell and with an alimentary canal open at both ends, and _Testicardines_ (_Articulata_), with a hinge between the dorsal and ventral valves and with no anus, was proposed by Owen and has been adopted by nearly all authors. In a later scheme based on our increased knowledge of fossil forms, the Brachiopoda are divided into four primary groups (orders). This is given at the end of the article, but it must not be forgotten that the existing forms with an anus (Ecardines) differ markedly from the aproctous members of the group (Testicardines).

1. _Magellania [Waldheimia] cranium_. A, ventral, B, dorsal valve.

2. _Rhynchonella (Hemithyris) psittacea_.

3. and 4. _Thecidea_.

5. _Spirifer_. Dorsal valve, showing calcareous spiral coils.

6. _Orthis calligramma_.

7. _Leptaena transversalis_. A, ventral, B, dorsal valve.

8. _Productus horridus_.

9. _Lingula pyramidata_ (after Morse).

10. _Discinisca lamellosa_.

11. _Crania anomala_ Interior of dorsal valve, showing muscular
impressions and labial appendages.]

The soft body of the Brachiopod is in all cases protected by a shell composed of two distinct valves; these valves are always, except in cases of malformation, equal-sided, but not equivalved. The valves are, consequently, essentially symmetrical, which is not the case with the Lamellibranchiata,--so much so, that certain Brachiopod shells were named _Lampades_, or lamp shells, by some early naturalists; but while such may bear a kind of resemblance to an antique Etruscan lamp, by far the larger number in no way resemble one. The shell is likewise most beautiful in its endless shapes and variations. In some species it is thin, semi-transparent and glassy, in others massive. Generally the shell is from a quarter of an inch to about 4 in. in size, but in certain species it attains nearly a foot in breadth by something less in length, as is the case with _Productus giganteus_. The valves are also in some species very unequal in their respective thickness, as may be seen in _Productus_ (_Daviesiella_)[1] _llangollensis_, _Davidsonia verneuilii_, &c., and while the space allotted to the animal is very great in many species, as in _Terebratula sphaeroidalis_, it is very small in others belonging to _Strophomena_, _Leptaena_, _Chonetes_, &c. The ventral valve is usually the thickest, and in some forms is six or seven times as great as the opposite one. The outer surface of many of the species presents likewise the most exquisite sculpture, heightened by brilliant shades, or spots of green, red, yellow and bluish black. Traces of the original colour have also been preserved in some of the fossil forms; radiating bands of a reddish tint have been often seen in well-preserved examples of _Terebratula_ (_Dielasma_) _hastata_, _T_. (_Dielasma_) _sacculus_, _T. communis_, _T. biplicata_, and of several others. Some specimens of _T. carnea_ are of a beautiful pale pink colour when first removed from their matrix, and E. Deslongchamps has described the tint of several Jurassic species.

The valves are distinguished as _dorsal_ and _ventral_. The ventral valve is usually the larger, and in many genera, such as _Terebratula_ and _Rhynchonella_, has a prominent beak or umbo, with a circular or otherwise shaped foramen at or near its extremity, partly bounded by one or two plates, termed a deltidium. Through the foramen passes a peduncle, by which the animal is in many species attached to submarine objects during at least a portion of its existence. Other forms show no indication of ever having been attached, while some that had been moored by means of a peduncle during the early portion of their existence have become detached at a more advanced stage of life, the opening becoming gradually cicatrized, as is so often seen in _Leptaena rhomboidalis_, _Orthisina anomala_, &c. Lastly, some species adhere to submarine objects by a larger or smaller portion of their ventral valve, as is the case with many forms of _Crania_, _Thecidium_, _Davidsonia_, &c. Some _Cranias_ are always attached by the whole surface of their lower or ventral valve, which models itself and fills up all the projections or depressions existing on either the rock, shell or coral to which it adhered. These irregularities are likewise, at times, reproduced on the upper or dorsal valve. Some species of _Strophalosia_ and _Productus_ seem also to have been moored during life to the sandy or muddy bottoms on which they lived, by the means of tubular spines often of considerable length. The interior of the shell varies very much according to families and genera. On the inner surface of both valves several well-defined muscular, vascular and ovarian impressions are observable; they form either indentations of greater or less size and depth, or occur as variously shaped projections. In the _Trimerellidae_, for example, some of the muscles are attached to a massive or vaulted platform situated in the medio-longitudinal region of the posterior half or umbonal portion of both valves. In addition to these, there exists in the interior of the _dorsal_ valve of some genera a variously modified, thin, calcified, ribbon-shaped skeleton for the support of the ciliated arms, and the form of this ribbon serves as one of the chief generic characters of both recent and extinct forms. This brachial skeleton is more developed in some genera than in others. In certain forms, as in _Terebratula_ and _Terebratulina_, it is short and simple, and attached to a small divided hinge-plate, the two riband-shaped lamina being bent upwards in the middle (fig. 15). The cardinal process is prominent, and on each side of the hinge-plate are situated the dental sockets; the loop in _Terebratulina_ becomes annular in the adult by the union of its crural processes (fig. 16). In _Magellania_ [_Waldheimia_] it is elongated and reflected; the hinge-plate large, with four depressions, under which originates a median septum, which extends more or less into the interior of the shell (figs. 13 and 14). In _Terebratella_ the loop is attached to the hinge-plate and to the septum (fig. 17). In _Megerlia_ it is three times attached, first to the hinge-plate, and then to the septum by processes from the diverging and reflected positions of the loop. In _Magas_ the brachial skeleton is composed of an elevated longitudinal septum reaching from one valve to the other, to which are affixed two pairs of calcareous lamellae, the lower ones riband-shaped; attached first to the hinge-plate, they afterwards proceed by a gentle curve near to the anterior portion of the septum, to the sides of which they are affixed; the second pair originate on both sides of the upper edge of the septum, extending in the form of two triangular anchor-shaped lamellae (fig. 18). In _Bouchardia_ the septum only is furnished with two short anchor-shaped lamellae. Many more modifications are observable in different groups of which the great family _Terebratulidae_ is composed. In _Thecidium_ (figs. 3,4) the interior of the dorsal valve is variously furrowed to receive the lophophore folded in two or more lobes. In the family _Spiriferidae_ there are two conical spires directed outwards, and nearly filling the cavity of the shell (fig. 5); while in _Atrypa_ the broad spirally coiled lamellae are vertical, and directed toward the centre of the dorsal valve. In the _Rhynchonellidae_ there are two short slender curved laminae, while in many genera and even families, such as the _Productidae, Strophomenidae, Lingulidae, Discinidae_, &c., there exists no calcified support for the labial appendages. The ventral valve in many of the genera is provided with two curved hinge-teeth, which fit into corresponding sockets in the opposite valve, so that the valves cannot be separated without breaking one of the teeth.

12. _Magellania [Waldheimia] flavescens_. Interior of ventral valve.
f, foramen; d, deltidium; t, teeth; a, adductor impressions (=
occlusors, _Hancock_); c, divaricator (= cardinal muscles, _King_, =
muscles diducteurs principaux, _Gratiolet_); c', accessory
divaricators (muscles diducteurs accessoires, _Gratiolet_); b, ventral
adjuster (= ventral peduncular muscles, or muscles du pedoncule paire
superieure, _Gratiolet_); b', peduncular muscle.

13. _Magellania [Waldheimia] flavescens_. Interior of dorsal valve. c,
c', cardinal process; b', b', hinge-plate; s, dental sockets; l, loop;
q, crura; a, a', adductor impressions; c, accessory divaricator; b,
peduncle muscles; ss, septum.

14. _Magellania [Waldheimia] flavescens_. Longitudinal section of
valves. A, ventral, B, dorsal valves; l, loop; q, crura; ss, septum;
c, cardinal process.

15. _Terebratula (Liothyris) vitrea_. Interior of dorsal valve. l,
loop; b, hinge-plate; c, cardinal process.

16. Loop of _Terebratulina caput serpentis_.

17. Longitudinal section of _Terebratella dorsata_. (References as in
fig. 14.)

18. Longitudinal section of _Magas pumilus_.]

flavescens_. Interior of dorsal valve, to show the position of the labial appendages. v, Mouth. (A portion of the fringe of cirri is removed to show the brachial membrane and a portion of the spiral extremities of the arms.)]

Each valve of the shell is lined by a mantle which contains prolongations of the body cavity. The outer surfaces of the mantle secrete the shell, which is of the nature of a cuticle impregnated by calcareous salts. These often have the form of prisms of calcite surrounded by a cuticular mesh work; the whole is nourished and kept alive by processes, which in _Crania_ are branched; these perforate the shell and permit the access of the coelomic fluid throughout its substance. These canals are closed externally and are absent in _Rhynchonella_, where the amount of calcareous deposit is small. In _Lingula_ the shell is composed of alternate layers of chitin and of phosphate of lime. The free edges of the mantle often bear chitinous bristles or setae which project beyond the shell. As in the case of the Lamellibranchiata, the shell of the adult is not a direct derivative of the youngest shell of the larva. The young Brachiopod in all its species is protected by an embryonic shell called the "protegulum," which sometimes persists in the umbones of the adult shells but is more usually worn off. In all species it has the same shape, a shape which has been retained in the adult by the Lower Cambrian genus _Iphidea_.

flavescens_. Logitudinal section with a portion of the animal.

d, h, Brachial appendages.
a, Adductor
c, c', Divaricator muscles.
s, Septum.
v, Mouth.
z, Exremity of alimentary tube. The penduncular muscules have been
purposely omitted.]

The body of the Brachiopod usually occupies about the posterior half of the space within the shell. The anterior half of this space is lined by the inner wall of the mantle and is called the mantle cavity. This cavity lodges the arms, which are curved and coiled in different ways in different genera. The water which bears the oxygen for respiration and the minute organisms upon which the Brachiopod feeds is swept into the mantle cavity by the action of the cilia which cover the arms, and the eggs and excreta pass out into the same cavity. The mouth lies in the centre of the anterior wall of the body. Its two lips fusing together at the corners of the mouth are prolonged into the so-called arms. These arms, which together form the lophophore, may be, as in _Cistella_, applied flat to the inner surface of the dorsal mantle fold, but more usually they are raised free from the body like a pair of moustaches, and as they are usually far too long to lie straight in the mantle cavity, they are folded or coiled up. The brachial skeleton which in many cases supports the arms has been mentioned above.

1. The ventral valve.
2. The dorsal valve.
3. The pedicle.
4. The mouth.
5. Lip which overhangs the mouth and runs all round the lophophore.
6. Tentacles.
7. Ovary in dorsal valve.
8. Liver diverticula.
9. Occlusor muscle--its double origin is shown.
10. Internal opening of left nephridium.
11. External opening of the same.
12. Ventral adjustor.
13. Divaricator muscle.
14. Sub-oesophageal nerve ganglion.
15. The heart.
16. Dorsal adjustor muscle.]

A transverse section through the arm (fig. 22) shows that it consists of a stout base, composed of a very hyaline connective tissue not uncommon in the tissues of the Brachiopoda, which is traversed by certain canals whose nature is considered below under the section (_The Body Cavity_) devoted to the coelom. Anteriorly this base supports a gurrie or gutter, the pre-oral rim of which is formed by a simple lip, but the post-oral rim is composed of a closely set row of tentacles. These may number some thousands, and they are usually bent over and tend to form a closed cylinder of the gutter. Each of these tentacles (fig. 22) is hollow, and it contains a diverticulum from the coelom, a branch of the vascular system, a nerve and some muscle-fibres. Externally on two sides and on the inner surface the tentacles are ciliated, and the cilia are continued across the gutter to the lip and even on the outer surface of the latter. These cilia pass on any diatoms and other minute organism which come within their range of action to the capacious oval mouth, which appears as a mere deepening of the gutter in the middle line. In _Terebratulina, Rhynchonella, Lingula_, and possibly other genera, the arms can be unrolled and protruded from the opened shell; in this case the tentacles also straighten themselves and wave about in the water.

_The Body Cavity._--The various internal organs of the brachiopod
body, the alimentary canal and liver, the excretory organs, the heart,
numerous muscles and the reproductive organs, are enclosed in a cavity
called the body cavity, and since this cavity (i.) is derived from the
archicoel and is from the first surrounded by meroblast, (ii.)
communicates with the exterior through the nephridia or excretory
organs, and (iii.) gives rise by the proliferation of the cells which
line it to the ova and spermatoza, it is of the nature of a true
coelom. The coelom then is a spacious chamber surrounding the
alimentary canal, and is continued dorsally and ventrally into the
sinuses of the mantle (fig. 21). Some of the endothelial cells lining
the coelom are ciliated, the cilia keeping the corpusculated fluid
contents in movement. Others of the endothelial cells show a great
tendency to form muscle fibres. Besides this main coelomic cavity
there are certain other spaces which F. Blochmann regards as coelomic,
but it must be remembered that his interpretation rests largely on
histological grounds, and at present embryological confirmation is
wanting. These spaces are as follows:--(i.) the great arm-sinus; (ii.)
the small arm-sinus together with the central sinus and the
peri-oesophageal sinus, and in _Discinisca_ and _Lingula_, and, to a
less extent, in _Crania_, the lip-sinus; (iii.) certain portions of
the general body cavity which in _Crania_ are separated off and
contain muscles, &c.; (iv.) the cavity of the stalk when such exists.
The great arm-sinus of each side of the lophophore lies beneath the
fold or lip which together with the tentacles forms the ciliated
groove in which the mouth opens. These sinuses are completely shut off
from all other cavities, they do not open into the main coelomic space
nor into the small arm-sinus, nor does the right sinus communicate
with the left. The small arm-sinus runs along the arms of the
lophophore at the base of the tentacles, and gives off a blind
diverticulum into each of these. This diverticulum contains the
blood-vessel and muscle-fibres (fig. 22). In the region of the mouth
where the two halves of the small arm-sinus approach one another they
open into a central sinus lying beneath the oesophagus and partly
walled in by the two halves of the ventral mesentery. This sinus is
continued round the oesophagus as the peri-oesophageal sinus, and thus
the whole complex of the small arm-sinus has the relations of the
so-called vascular system of a Sipunculid. In _Crania_ it is
completely shut off from the main coelom, but in _Lingula_ it
communicates freely with this cavity. In _Discinisca_ and _Lingula_
there is further a lip-sinus or hollow system of channels which
traverses the supporting tissue of the edge of the mantle and contains
muscle-fibres. It opens into the peri-oesophageal sinus. It is better
developed and more spacious in _Lingula_ than in _Discinisca._ In
_Crania_, where only indications of the lip-sinus occur, there are two
other closed spaces. The posterior occlusor muscles lie in a special
closed space which Blochmann also regards as coelomic. The posterior
end of the intestine is similarly surrounded by a closed coelomic
space known as the peri-anal sinus in which the rectum lies freely,
unsupported by mesenteries. All these spaces contain a similar
coagulable fluid with sparse corpuscles, and all are lined by ciliated
cells. There is further a great tendency for the endothelial cells to
form muscles, and this is especially pronounced in the small
arm-sinus, where a conspicuous muscle is built up. The mantle-sinuses
which form the chief spaces in the mantle are diverticula of the main
coelomic cavity. In _Discinisca_ they are provided with a muscular
valve placed at their point of origin. They contain the same fluid as
the general coelom. The stalk is an extension of the ventral
body-wall, and contains a portion of the coelom which, in _Discinisca_
and _Lingula_, remains in communication with the general body cavity.

1. The lip.
2. The base of a tentacle bisected in the middle line.
3. Great arm-sinus.
4. Small arm-sinus, containing muscle-fibres.
5. Tentacular canal.
6. External tentacular muscle.
7. Tentacular blood-vessel arising from the cut arm-vessel in the
small arm-sinus.
8. Chief arm-nerve.
9. Secondary arm-nerve.
10. Under arm-nerve.]

_The Alimentary Canal_.--The mouth, which is quite devoid of armature,
leads imperceptibly into a short and dorsally directed oesophagus. The
latter enlarges into a spherical stomach into which open the broad
ducts of the so-called liver. The stomach then passes into an
intestine, which in the Testicardines (Articulata) is short,
finger-shaped and closed, and in the Ecardines (Inarticulata) is
longer, turned back upon its first course, and ends in an anus. In
_Lingula_ and _Discina_ the anus lies to the right in the
mantle-cavity, but in _Crania_ it opens medianly into a posterior
extension of the same. Apart from the asymmetry of the intestine
caused by the lateral position of the anus in the two genera just
named, Brachiopods are bilaterally symmetrical animals.

The liver consists of a right and left half, each opening by a broad
duct into the stomach. Each half consists of many lobes which may
branch, and the whole takes up a considerable proportion of the space
in the body cavity. The food passes into these lobes, which may be
found crowded with diatoms, and without doubt a large part of the
digestion is carried on inside the liver. The stomach, oesophagus and
intestine are ciliated on their inner surface. The intestine is slung
by a median dorsal and ventral mesentery which divides the body cavity
into two symmetrically shaped halves; it is "stayed" by two transverse
septa, the anterior or gastroparietal band running from the stomach to
the body wall and the posterior or ileoparietal band running from the
intestine to the body wall. None of these septa is complete, and the
various parts of the central body cavity freely communicate with one
another. In _Rhynchonella_, where there are two pairs of kidneys, the
internal opening of the anterior pair is supported by the
gastroparietal band and that of the posterior pair by the ileoparietal
band. The latter pair alone persists in all other genera.

The kidneys or nephridia open internally by wide funnel-shaped
nephridiostomes and externally by small pores on each side of the
mouth near the base of the arms. Each is short, gently curved and
devoid of convolutions. They are lined by cells charged with a yellow
or brown pigment, and besides their excretory functions they act as
ducts through which the reproductive cells leave the body.

_Circulatory System._--The structures formerly regarded as
pseudohearts have been shown by Huxley to be nephridia; the true heart
was described and figured by A. Hancock, but has in many cases escaped
the observation of later zoologists. F. Blochmann in 1884, however,
observed this organ in the living animal in species of the following
genera:--_Terebratulina, Magellania_ [_Waldheimia_]_, Rhynchonella,
Megathyris_ (_Argiope_), _Lingula_, and _Crania_ (fig. 21). It
consists of a definite contractile sac or sacs lying on the dorsal
side of the alimentary canal near the oesophagus, and in preparations
of _Terebratulina_ made by quickly removing the viscera and examining
them in sea-water under a microscope, he was able to count the
pulsations, which followed one another at intervals of 30-40 seconds.

A vessel--the dorsal vessel--runs forward from the heart along the
dorsal surface of the oesophagus. This vessel is nothing but a split
between the right and left folds of the mesentery, and its cavity is
thus a remnant of the blastocoel. A similar primitive arrangement is
thought by F. Blochmann to obtain in the genital arteries. Anteriorly
the dorsal vessel splits into a right and a left half, which enter the
small arm-sinus and, running along it, give off a blind branch to each
tentacle (fig. 21). The right and left halves are connected ventrally
to the oesophagus by a short vessel which supplies these tentacles in
the immediate neighbourhood of the mouth. There is thus a vascular
ring around the oesophagus. The heart gives off posteriorly a second
median vessel which divides almost at once into a right and a left
half, each of which again divides into two vessels which run to the
dorsal and ventral mantles respectively. The dorsal branch sends a
blind twig into each of the diverticula of the dorsal mantle-sinus,
the ventral branch supplies the nephridia and neighbouring parts
before reaching the ventral lobe of the mantle. Both dorsal and
ventral branches supply the generative organs.

The blood is a coagulable fluid. Whether it contains corpuscles is not
yet determined, but if so they must be few in number. It is a
remarkable fact that in _Discinisca_, although the vessels to the
lophophore are arranged as in other Brachiopods, no trace of a heart
or of the posterior vessels has as yet been discovered.

_Muscles._--The number and position of the muscles differ materially
in the two great divisions into which the Brachiopoda have been
grouped, and to some extent also in the different genera of which each
division is composed. Unfortunately almost every anatomist who has
written on the muscles of the Brachiopoda has proposed different names
for each muscle, and the confusion thence arising is much to be
regretted. In the Testicardines, of which the genus _Terebratula_ may
be taken as an example, five or six pairs of muscles are stated by A.
Hancock, Gratiolet and others to be connected with the opening and
closing of the valves, or with their attachment to or movements upon
the peduncle. First of all, the adductors or occlusors consist of two
muscles, which, bifurcating near the centre of the shell cavity,
produce a large quadruple impression on the internal surface of the
small valve (fig. 13, a, a'), and a single divided one towards the
centre of the large or ventral valve (fig. 12, a). The function of
this pair of muscles is the closing of the valves. Two other pairs
have been termed _divaricators_ by Hancock, or _cardinal muscles_
("muscles diducteurs" of Gratiolet), and have for function the opening
of the valves. The divaricators proper are stated by Hancock to arise
from the ventral valve, one on each side, a little in advance of and
close to the adductors, and after rapidly diminishing in size become
attached to the cardinal process, a space or prominence between the
sockets in the dorsal valve. The _accessory divaricators_ are,
according to the same authority, a pair of small muscles which have
their ends attached to the ventral valve, one on each side of the
median line, a little behind the united basis of the adductors, and
again to the extreme point of the cardinal process. Two pairs of
muscles, apparently connected with the peduncle and its limited
movements, have been minutely described by Hancock as having one of
their extremities attached to this organ. The _dorsal adjusters_ are
fixed to the ventral surface of the peduncle, and are again inserted
into the hinge-plate in the smaller valve. The _ventral adjusters_ are
considered to pass from the inner extremity of the peduncle, and to
become attached by one pair of their extremities to the ventral valve,
one on each side and a little behind the expanded base of the
divaricators. The function of these muscles, according to the same
authority, is not only that of erecting the shell; they serve also to
attach the peduncle to the shell, and thus effect the steadying of it
upon the peduncle. By alternate contracting they can cause a slight
rotation of the animal in its stalk.

flavescens_. Diagram
showing the muscular system. (After Hancock.)

M, Ventral,
N, Dorsal valve,
l, Loop.
V, Mouth.
Z, Extremity of intestine,
c, Divaricators.
c', Accessory divaricators.
a, Adductor.
b, Ventral adjusters.
b', Peduncular muscles.
b'', Dorsal adjusters.
P, Peduncle.]

Such is the general arrangement of the shell muscles in the division
composing the articulated Brachiopoda, making allowance for certain
unimportant modifications observable in the animals composing the
different families and genera thereof. Owing to the strong and tight
interlocking of the valves by the means of curved teeth and sockets,
many species of Brachiopoda could open their valves but slightly. In
some species, such as _Thecidea_, the animal could raise its dorsal
valve at right angles to the plane of the ventral one (fig. 4).

25, Interior of ventral valve.
26, Interior of dorsal valve.
g, Umbonal muscular impressions (open valves).
h, Central muscles (close valves).
i, Transmedial or sliding muscles.
b, Parietal band.
j, k, l, Lateral muscles (j, anteriors; k, middles; l, outsiders),
enabling the valves to move forward and backward on each other.

(After King.)]

In the Ecardines, of which _Lingula_ and _Discina_ may be quoted as
examples, the myology is much more complicated. Of the shell or
valvular muscles W. King makes out five pairs and an odd one, and
individualizes their respective functions as follows:--Three pairs are
_lateral_, having their members limited to the sides of the shell; one
pair are _transmedians_, each member passing across the middle of the
reverse side of the shell, while the odd muscle occupies the umbonal
cavity. The _central_ and _umbonal_ muscles effect the direct opening
and closing of the shell, the _laterals_ enable the valves to move
forward and backward on each other, and the _transmedians_ allow the
similar extremities (the rostral) of the valves to turn from each
other to the right or the left on an axis subcentrically situated,
that is, the medio-transverse region of the dorsal valve. It was long
a matter in discussion whether the animal could displace its valves
sideways when about to open its shell, but this has been actually
observed by Professors K. Semper and E.S. Morse, who saw the animal
perform the operation. They mention that it is never done suddenly or
by jerks, as the valves are at first always pushed to one side several
times and back again on each other, at the same time opening gradually
in the transverse direction till they rest opposite to one another and
widely apart. Those who have not seen the animal in life, or who did
not believe in the possibility of the valves crossing each other with
a slight obliquity, would not consent to appropriating any of its
muscles to that purpose, and consequently attributed to all the
lateral muscles the simple function of keeping the valves in an
opposite position, or holding them adjusted. We have not only the
observations of Semper and Morse, but the anatomical investigations of
King, to confirm the sliding action or lateral divarication of the
valves of _Lingula_.

Diagram showing the muscular system. (After Hancock.) The letters
indicate the muscles as in figs. 25 and 26.

A, Dorsal,
B, Ventral valve.
p, Peduncle.
e, Heart.
a, Alimentary tube.
z, Anal aperture.]

In the Testicardines, where no such sliding action of the valves was
necessary or possible, no muscles for such an object were required,
consequently none took rise from the lateral portions of the valves as
in _Lingula_; but in an extinct group, the _Trimerellidae_, which
seems to be somewhat intermediate in character between the Ecardines
and Testicardines, have been found certain scars, which appear to have
been produced by rudimentary lateral muscles, but it is doubtful
(considering the shells are furnished with teeth, though but rudely
developed) whether such muscles enabled the valves, as in _Lingula_,
to move forward and backward upon each other. _Crania_ in life opens
its valves by moving upon the straight hinge, without sliding the
valve.

The _nervous system_ of Brachiopods has, as a rule, maintained its
primitive connexion with the external epithelium. In a few places it
has sunk into the connective-tissue supporting layer beneath the
ectoderm, but the chief centres still remain in the ectoderm, and the
fibrils forming the nerves are for the most part at the base of the
ectodermal cells. Above the oesophagus is a thin commissure which
passes laterally into the chief arm-nerve. This latter includes in its
course numerous ganglion cells, and forms, according to F. Blochmann,
the immensely long drawn out supra-oesophageal ganglion. The chief
arm-nerve traverses the lophophore, being situated between the great
arm-sinus and the base of the lip (figs. 22 and 28); it gives off a
branch to each tentacle, and these all anastomose at the base of the
tentacles with the second nerve of the arm, the so-called secondary
arm-nerve. Like the chief arm-nerve, this strand runs through the
lophophore, parallel indeed with the former except near the middle
line, where it passes ventrally to the oesophagus. The lophophore is
supplied by yet a third nerve, the under arm-nerve, which is less
clearly defined than the others, and resembles a moderate aggregation
of the nerve fibrils, which seem everywhere to underlie the ectoderm,
and which in a few cases are gathered up into nerves. The under
arm-nerve, which lies between the small arm-sinus and the surface,
supplies nerves to the muscles of both arm-sinuses (figs. 22 and 28).
Medianly, it has its origin in the sub-oesophageal ganglion, which,
like the supra-oesophageal, is drawn out laterally, though not to the
same extent. In the middle line the sub-oespphageal nerve mass is
small; the ganglion is in fact drawn out into two halves placed on
either side of the body. From each of these sub-oesophageal ganglia
numerous nerves arise. Passing from the middle line outwards they
are--(i.) the median pallial nerve to the middle of the dorsal mantle;
(ii.) numerous small nerves--the circum-oesophageal commissures--which
pass round the oesophagus to the chief arm-nerve or supra-oesophageal
ganglion; (iii.) the under arm-nerve to the lophophore and its
muscles; (iv.) the lateral pallial nerve to the sides of the dorsal
mantle. Laterally, the sub-oesophageal ganglia give off (v.) nerves to
the ventral mantle, and finally they supply (vi.) branches to the
various muscles. There is a special marginal nerve running round the
edge of the mantle, but the connexion of this with the rest of the
nervous system is not clear; probably it is merely another
concentration of the diffused sub-ectodermal nervous fibrils.

The above account applies more particularly to _Crania_, but in the
main it is applicable to the other Inarticulata which have been
investigated. In _Discinisca_ and _Lingula_, however, the
sub-oesophageal ganglion is not drawn out, but lies medianly; it gives
off two posteriorly directed nerves to the stalk, which in _Lingula_
unite and form a substantial nerve. Sense organs are unknown in the
adult. The larval forms are provided with eye-spots, but no very
specialized sense organs are found in the adult.

1. Oesophagus.
2. Supra-oesophageal commisure.
3. Circum-oesophageal commisure.
4. Under arm-nerve.
5. Great arm-sinus.
6. Small arm-sinus.
7. Tentacle.
8. Lip of lophophore.
9. Infra-oesophageal commisure.
10. Chief arm-nerve.
11. Secondary arm-nerve.
12. Nerves to tentacles.
13. Sub-oesophageal ganglion.
14. Dorsal lateral nerve.
15. Sub-oesophageal portion of the secondary arm-nerve.
16. Median pallial nerve of dorsal lobe of mantle.
17. Anterior occlusor muscle.
18. Posterior occlusor muscle.
19. Obliquus superior muscle.
20. Levator brachii muscle.]

The _histology_ of Brachiopods presents some peculiar and many
primitive features. As a rule the cells are minute, and this has
especially stood in the way of embryological research. The plexus of
nerve-fibrils which underlie the ectoderm and are in places gathered
up into nerves, and the great development of connective tissue, are
worthy of notice. Much of the latter takes the form of hyaline
supporting tissue, embedded in which are scattered cells and fibres.
The lophophore and stalk are largely composed of this tissue. The
ectodermal cells are large, ciliated, and amongst the ciliated cells
glandular cells are scattered. The chitinous chaetae have their origin
in special ectodermal pits, at the base of which is one large cell
which is thought to secrete the chaeta, as in Chaetopods. These pits
are not isolated, but are connected by an ectodermal ridge, which
grows in at the margin of the mantle and forms a continuous band
somewhat resembling the ectodermal primordium of vertebrate teeth.

The ovary and testes are heaped-up masses of red or yellow cells due
to a proliferation of the cells lining the coelom. There are four of
such masses, two dorsal and two ventral, and as a rule they extend
between the outer and inner layer of the mantle lining the shells. The
ova and the spermatozoa dehisce into the body cavity and pass to the
exterior through the nephridia. Fertilization takes place outside the
body, and in some species the early stages of development take place
in a brood-pouch which is essentially a more or less deep depression
of the body-wall median in _Thecidea_, while in _Cistella_ (_?
Argiope_) there is one such pouch on each side, just below the base of
the arms, and into these the nephridia open. The developing ova are
attached by little stalks to the walls of these pouches. In spite of
some assertions to the contrary, all the Brachiopods which have been
carefully investigated have been found to be male or female.
Hermaphrodite forms are unknown.

[FIG. 29.--Three larvae stages of _Megathyris_ (_Argiope_). A, Larva
which has just left brood-pouch; B, longitudinal section through a
somewhat later stage; C, the fully formed embryo just before
fixing--the neo-embryo of Beecher. Highly magnified.

1. Anterior segment.
2. Second or mantle-forming segment.
3. Third or stalk-forming segment.
4. Eye-spots.
5. Setae.
6. Nerve mass (?).
7. Alimentary canal.
8. Muscles.]

_Embryology._--With the exception of Yatsu's article on the
development of _Lingula_ (_J. Coll. Sci., Japan_, xvii., 1901-1903)
and E.G. Conklin's on "Terebratulina septentrionalis" (_P. Amer. Phil.
Soc._ xli., 1902), little real advance has been made in our knowledge
of the embryology of the Brachiopoda within recent years. Kovalevsky's
researches (Izv. Obshch. Moskov, xiv., 1874) on _Megathyris_
(_Argiope_) and Yatsu's just mentioned are the most complete as
regards the earlier stages. Segmentation is complete, a gastrula is
formed, the blastopore closes, the archenteron gives off two coelomic
sacs which, as far as is known, are unaffected by the superficial
segmentation of the body that divides the larva into three segments.
The walls of these sacs give rise at an early stage to muscles which
enable the parts of the larva to move actively on one another (fig.
29, B). About this stage the larvae leave the brood-pouch, which is a
lateral or median cavity in the body of the female, and lead a free
swimming life in the ocean. The anterior segment broadens and becomes
umbrella-shaped; it has a powerful row of cilia round the rim and
smaller cilia on the general surface. By the aid of these cilia the
larva swims actively, but owing to its minute size it covers very
little distance, and this probably accounts for the fact that where
brachiopods occur there are, as a rule, a good many in one spot. The
head bears four eye-spots, and it is continually testing the ground
(fig. 29, A, C). The second segment grows downwards like a skirt
surrounding the third segment, which is destined to form the stalk. It
bears at its rim four bundles of very pronounced chaetae. After a
certain time the larva fixes itself by its stalk to some stone or
rock, and the skirt-like second segment turns forward over the head
and forms the mantle. What goes on within the mantle is unknown, but
presumably the head is absorbed. The chaetae drop off, and the
lophophore is believed to arise from thickenings which appear in the
dorsal mantle lobe. The Plankton Expedition brought back, and H.
Simroth (_Ergeb. Plankton Expedition_, ii., 1897) has described, a few
larval brachiopods of undetermined genera, two of which at least were
pelagic, or at any rate taken far from the coast. These larvae, which
resemble those described by Fritz Muller (_Arch. Naturg._, 1861-1862),
have their mantle turned over their head and the larval shell well
developed. No stalk has been seen by Simroth or Fritz Muller, but in
other respects the larva resembles the stages in the development of
_Megathyris_ and _Terebratulina_ which immediately precede fixation.
The cirri or tentacles, of which three or four pairs are present, are
capable of being protruded, and the minute larva swims by means of the
ciliary action they produce. It can retract the tentacles, shut its
shell, and sink to the bottom.

[FIG. 30.--Stages in the fixing and metamorphosis of _Terebratulina_.
Highly magnified. (From Morse.)

A, Larva (neo-embryo) just come to rest.
B, C, D, Stages showing the turning forward of the second or mantle
segment.
E, Completion of this.
F, Young Brachiopod.
1, 2, 3, The first, second and third segments.]

C.E.E. Beecher (_Amer. Jour. Sci._ ser. 3, xli. and xliv.) has
classified with appropriate names the various stages through which
Brachiopod larvae pass. The last stage, that in which the folds of the
second segment are already reflected over the first, he calls the
Typembryo. Either before or just after turning, the mantle develops a
larval shell termed the protegulum, and when this is completed the
larva is termed the Phylembryo. By this time the eyes have
disappeared, the four bundles of chaetae have dropped off, and the
lophophore has begun to appear as an outgrowth of the dorsal mantle
lobe. The protegulum has been found in members of almost all the
families of Brachiopod, and it is thought to occur throughout the
group. It resembles the shell of the Cambrian genus _Iphidea
[Paterina]_, and the Phylembryo is frequently referred to as the
_Paterina_ stage. In some orders the Phylembryo is succeeded by an
_Obolella_ stage with a nearly circular outline, but this is not
universal. The larva now assumes specific characters and is
practically adult.

[FIG. 31.--Shell of larval Brachiopod. Phylembryo stage. (From
Simroth.) 1, Protegulum; 2, permanent shell.]

_Classification_.--Beecher's division of the Brachiopoda into four
orders is based largely on the character of the aperture through which
the stalk or pedicle leaves the shell. To appreciate his diagnoses it
is necessary to understand certain terms, which unfortunately are not
used in the same sense by all authors. The triangular pedicle-opening
seen in _Orthis_, &c., has been named by James Hall and J.M. Clarke
the delthyrium. In some less primitive genera, e.g. _Terebratula_,
that type of opening is found in the young stages only; later it
becomes partly closed by two plates which grow out from the sides of
the delthyrium. These plates are secreted by the ventral lobe of the
mantle, and were named by von Buch in 1834 the "deltidium." The form
of the deltidium varies in different genera. The two plates may meet
in the middle line, and leave only a small oval opening near the
centre for the pedicle, as in _Rhynchonella_; or they may meet only
near the base of the delthyrium forming the lower boundary of the
circular pedicle-opening, as in _Terebratula_; or the right plate may
remain quite distinct from the left plate, as in _Terebratella_. The
pro-deltidium, a term introduced by Hall and Clarke, signifies a small
embryonic plate originating on the dorsal side of the body. It
subsequently becomes attached to the ventral valve, and develops into
the pseudo-deltidium, in the Neotremata and the Protremata. The
pseudo-deltidium (so named by Bronn in 1862) is a single plate which
grows from the apex of the delthyrium downwards, and may completely
close the aperture. The pseudo-deltidium is sometimes reabsorbed in
the adult. In the Telotremata neither pro-deltidium nor
pseudo-deltidium is known. In the Atremata the pro-deltidium does not
become fixed to the ventral valve, and does not develop into a
pseudo-deltidium. The American use of the term deltidium for the
structure which Europeans call the pseudo-deltidium makes for
confusion. The development of the brachial supports has been studied
by Friele, Fischer and Oehlert. A summary of the results is given by
Beecher (_Trans. Connect. Acad._ ix., 1893; reprinted in _Studies in
Evolution_, 1901).

The orders Atremata and Neotremata are frequently grouped together, as
the sub-class Inarticulata or Ecardines--the Tretenterata of
Davidson--and the orders Protremata and Telotremata, as the Articulata
or Testicardines--the Clistenterata of Davidson. The following scheme
of classification is based on Beecher's and Schubert's. Recent
families are printed in italic type.

[FIG. 32.--Diagram of the pedicle-opening of _Rhynchonella_. Magnified.

1. Umbo of ventral valve.
2. Deltidium.
3. Margin of delthyrium.
4. Pedicle-opening.
5. Dorsal valve.]

Class I. ECARDINES (INARTICULATA)

ORDER I. Atremata (Beecher).--Inarticulate Brachiopoda, with the
pedicle passing out between the umbones, the opening being shared by
both valves. Pro-deltidium attached to dorsal valves.
FAMILIES.--PATERINIDAE, OBOLIDAE, TRIMERELLIDAE, LINGULELLIDAE,
_LINGULIDAE_, LIGULASMATIDAE.

ORDER II. Neotremata (Beecher).--More or less circular, cone-shaped,
inarticulate Brachiopoda. The pedicle passes out at right angles to
the plane of junction of the valves of the shell; the opening is
confined to the ventral valve, and may take the form of a slit, or may
be closed by the development of a special plate called the listrium,
or by a pseudo-deltidium. Pro-deltidium attached to ventral valve.
FAMILIES.--ACROTRETIDAE, SIPHONOTRETIDAE, TREMATIDAE, _DISCINIDAE_,
_CRANIIDAE_.

Class II. TESTICARDINES (ARTICULATA)

ORDER III. Protremata (Beecher).--Articulate Brachiopoda, with
pedicle-opening restricted to ventral valve, and either open at the
hinge line or more or less completely closed by a pseudo-deltidium,
which may disappear in adult. The pro-deltidium originating on the
dorsal surface later becomes anchylosed with the ventral valve.
FAMILIES.--KUTORGINIDAE, EICHWALDIIDAE, BILLINGSELLIDAE,
STROPHOMENIDAE, _THECIDIIDAE_, PRODUCTIDAE, RICHTHOFENIDAE, ORTHIDAE,
CLITAMBONITIDAE, SYNTROPHIIDAE, PORAMBONITIDAE, PENTAMERIDAE.

ORDER IV. Telotremata (Beecher).--Articulate Brachiopoda, with the
pedicle-opening, confined in later life to the ventral valve, and
placed at the umbo or beneath it. Deltidium present, but no
pro-deltidium. Lophophore supported by calcareous loops, &c.
FAMILIES.--PROTORHYNCHIDAE, _RHYNCHONELLIDAE_, CENTRONELLIDAE,
_TEREBRATULIDAE_, STRINGOCEPHALIDAE, MEGALANTERIDAE,
_TEREBRATELLIDAE_, ATRYPIDAE, SPIRIFERIDAE, ATHYRIDAE.

_Affinities_.--Little light has been thrown on the affinities of the
Brachiopoda by recent research, though speculation has not been
wanting. Brachiopods have been at various times placed with the
Mollusca, the Chaetopoda, the Chaetognatha, the Phoronidea, the
Polyzoa, the Hemichordata, and the Urochordata. None of these
alliances has borne close scrutiny. The suggestion to place
Brachiopods with the Polyzoa, _Phoronis, Rhabdopleura_ and
_Cephalodiscus_, in the Phylum Podaxonia made in _Ency. Brit._ (vol.
xix, ninth edition, pp. 440-441) has not met with acceptance, and
until we have a fuller account of the embryology of some one form,
preferably an Inarticulate, it is wiser to regard the group as a very
isolated one. It may, however, be pointed out that Brachiopods seem to
belong to that class of animal which commences life as a larva with
three segments, and that tri-segmented larvae have been found now in
several of the larger groups.

_Distribution._--Brachiopods first appear in the Lower Cambrian, and
reached their highest development in the Silurian, from which upwards
of 2000 species are known, and were nearly as numerous in the Devonian
period; at present they are represented by some 140 recent species.
The following have been found in the British area, as defined by A.M.
Norman, _Terebratulina caput-serpentis_ L., _Terebratula (Gwynia)
capsula_ Jeff., _Magellania (Macandrevia) cranium_ Mull., _M.
septigera_ Loven, _Terebratella spitzbergenensis_ Dav., _Megathyris
decollata_ Chemn., _Cistella cistellula_ S. Wood, _Cryptopora gnomon_
Jeff., _Rhynchonella (Hemithyris) psittacea_ Gmel., _Crania anomala_
Mull., and _Discinisca atlantica_ King. About one-half the 120
existing species are found above the 100-fathoms line. Below 150
fathoms they are rare, but a few such as _Terebratulina wyvillei_ are
found down to 2000 fathoms. _Lingula_ is essentially a very shallow
water form. As a rule the genera of the northern hemisphere differ
from those of the southern. A large number of specimens of a species
are usually found together, since their only mode of spreading is
during the ciliated larval stage, which although it swims vigorously
can only cover a few millimetres an hour; still it may be carried some
little distance by currents.

Undue stress is often laid on the fact that _Lingula_ has come down to
us apparently unchanged since Cambrian times, whilst _Crania_, and
forms very closely resembling _Discina_ and _Rhynchonella_, are found
from the Ordovician strata onwards. The former statement is, however,
true of animals from other classes at least as highly organized as
Brachiopods, e.g. the Gasteropod _Capulus_, whilst most of the
invertebrate classes were represented in the Ordovician by forms which
do not differ from their existing representatives in any important
respect.

A full bibliography of Brachiopoda (recent and fossil) is to be found
in Davidson's Monograph of British Fossil Brachiopods, _Pal. Soc.
Mon._ vi., 1886. The Monograph on Recent Brachiopoda, by the same
author, _Tr. Linn. Soc. London_, Zool. ser. ii. vol. iv., 1886-1888,
must on no account be omitted. (A. E. S.)

FOOTNOTE:

[1] Subgenera are indicated by round, synonyms by square brackets.

BRACHISTOCHRONE (from the Gr. [Greek: brachistos], shortest, and [Greek: chronos], time), a term invented by John Bernoulli in 1694 to denote the curve along which a body passes from one fixed point to another in the shortest time. When the directive force is constant, the curve is a cycloid (q.v.); under other conditions, spirals and other curves are described (see MECHANICS).

BRACHYCEPHALIC (Gr. for short-headed), a term invented by Andreas Retzius to denote those skulls of which the width from side to side was little less than the length from front to back, their ratio being as 80 to 100, as in those of the Mongolian type. Thus taking the length as 100, if the width exceeds 80, the skull is to be classed as brachycephalic. The prevailing form of the head of civilized races is brachycephalic. It is supposed that a brachycephalic race inhabited Europe before the Celts. Among those peoples whose heads show marked brachycephaly are the Indo-Chinese, the Savoyards, Croatians, Bavarians, Lapps, Burmese, Armenians and Peruvians. (See CRANIOMETRY.)

BRACKYLOGUS (from Gr. [Greek: brachys], short, and [Greek: logos], word), title applied in the middle of the 16th century to a work containing a systematic exposition of the Roman law, which some writers have assigned to the reign of the emperor Justinian, and others have treated as an apocryphal work of the 16th century. The earliest extant edition of this work was published at Lyons in 1549, under the title of _Corpus Legum per modum Institutionum_; and the title _Brachylogus totius Juris Civilis_ appears for the first time in an edition published at Lyons in 1553. The origin of the work may be referred with great probability to the 12th century. There is internal evidence that it was composed subsequently to the reign of Louis le Debonnaire (778-840), as it contains a Lombard law of that king's, which forbids the testimony of a clerk to be received against a layman. On the other hand its style and reasoning is far superior to that of the law writers of the 10th and 11th centuries; while the circumstance that the method of its author has not been in the slightest degree influenced by the school of the Gloss-writers (Glossatores) leads fairly to the conclusion that he wrote before that school became dominant at Bologna. Savigny, who traced the history of the _Brachylogus_ with great care, is disposed to think that it is the work of Irnerius himself (_Geschichte des rom. Rechts im Mittelalter_). Its value is chiefly historical, as it furnishes evidence that a knowledge of Justinian's legislation was always maintained in northern Italy. The author of the work has adopted the _Institutes_ of Justinian as the basis of it, and draws largely on the _Digest_, the _Code_ and the _Novels_; while certain passages, evidently taken from the _Sententiae Receptae_ of Julius Paulus, imply that the author was also acquainted with the Visigothic code of Roman law compiled by order of Alaric II.

An edition by E. Bocking was published at Berlin in 1829, under the
title of _Corpus Legum sive Brachylogus Juris Civilis_. See also H.
Fitting, _Uber die Heimath und das Alter des sogenannten Brachylogus_
(Berlin, 1880).

BRACKET, in architecture and carpentering, a projecting feature either in wood or metal for holding things together or supporting a shelf. The same feature in stone is called a "console" (q.v.). In furniture it is a small ornamental shelf for a wall or a corner, to bear knick-knacks, china or other bric-a-brac. The word has been referred to "brace," clamp, Lat. _bracchium_, arm, but the earliest form "bragget" (1580) points to the true derivation from the Fr. _braguette_, or Span. _bragueta_ (Lat. _bracae_, breeches), used both of the front part of a pair of breeches and of the architectural feature. The sense development is not clear, but it has no doubt been influenced by the supposed connexion with "brace."