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upper limb reacting on the form of the bone of that side. The influence of muscular action, however, does not wholly account for the production of the curves of the bone, since the bone has been shown to display its characteristic features in cases where there has been defective development or absence of the upper limb (Reynault). Partial or complete absence of the clavicle has been recorded. W. S. Taylor exhibited an interesting case of this kind at the Clinical Society of London, October 25, 1901. Sometimes there is a small canal through the anterior border of the bone near its middle for the transmission of one of the supra-clavicular nerves.
Scapula. The most common variation met with is a separated acromion. In these cases there has been failure in the ossific union between the spine and acromion, the junction between the two being effected by a layer of cartilage or by an articulation possessing a joint cavity. The condition is usually symmetrical on both sides, though instances are recorded where this arrangement is unilateral. Very much rarer is the condition in which the coracoid process is separable from the rest of the bone. The size and form of the scapular notch differs. In certain cases the superior border of the bone describes a uniform curve reaching the base of the coracoid without any indication of a notch. In some scapula, more particularly in those of very old people, the floor of the subscapular fossa is deficient owing to the absorption of the thin bone, the periosteal layers alone filling up the gap.
At birth the vertical length of the bone is less in proportion to its width than in the adult. Humerus. As has been stated in the description of the bone, the olecranon and coronoid fosse may communicate with each other in the macerated bone. The resulting supratrochlear foramen is most commonly met with in the lower races of man, as well as in the anthropoid apes, and in some other mammals. The occurrence of a hook-like spine, called the epicondylic process, which projects in front of the medial epicondylic ridge, is not uncommon. Its extremity is connected with the medial epicondyle by means of a fibrous band, underneath which the median nerve, accompanied by the brachial artery, or one of its large branches, may pass, or in some instances, the nerve alone, or the artery unaccompanied by the nerve. This arrangement is the homologue in a rudimentary form of a canal present in many animals, notably in the carnivora and marsupials. In addition to the broad radial groove already described, and which is no doubt produced by the twisting or torsion of the body, there is occasionally a distinct narrow groove posterior to it, which marks precisely the course of the radial nerve as it turns round the lateral side of the body of the bone.
Ulna.-Cases of partial or complete absence of the ulna through congenital defect have been recorded. Rosenmüller has described a case in which the olecranon was separated from the proximal end of the bone, resembling thus in some respects the patella. In powerfully developed bones there is a tendency to the formation of a sharp projecting crest corresponding to the insertion of the triceps.
Radius.-Cases of congenital absence of the radius are recorded; in these the thumb is not infrequently wanting as well.
Carpus. Increase in the number of the carpal elements is occasionally met with, and these have been ascribed to division of the navicular, os lunatum, os triquetrum, capitate, lesser multangular, and os hamatum. Of these the most interesting is the os centrale, first described by Rosenberg, and subsequently investigated by Henke, Leboucq, and others. This is met with almost invariably as an independent cartilaginous element during the earlier months of fœtal life, and occasionally becomes developed into a distinct ossicle placed on the back of the carpus between the navicular and capitate bones and the lesser multangular. Its significance depends on the fact that it is an important component of the carpus in most mammals, and is met with normally in the orang and most monkeys. Ordinarily in man, as was pointed out by Leboucq, it becomes fused with the navicular, where its presence is often indicated by a small tubercle, a condition which obtains in the chimpanzee, the gorilla, and the gibbons. Dwight has described a case in which there was an os subcapitulum in both hands. The ossicle lay between the base of the middle metacarpal bone and the capitate bone, with the lesser multangular to its radial side. (Anat. Anz. vol. xxiv.) Further addition to the number of the carpal elements may be due to the separation of the styloid process of the third metacarpal bone and its persistence as a separate ossicle.
Reduction in the number of the carpus has been met with, but this is probably due to pathological causes. Morestin (Bull. Soc. Anat. de Paris, tome 71, p. 651), who has investigated the subject, finds that ankylosis occurs most frequently between the bases of the second and third metacarpal bones and the carpus, seldom or never between the carpus and the first metacarpal, or between the pisiform and os triquetrum. Instances of complete fusion of the os lunatum and triquetral bones, without any apparent pathological change, have been recorded in Europeans, Negroes, and an Australian.
Metacarpal Bones. -As previously stated above, the styloid process of the third metacarpal bone appears as a separate ossicle in about 18 per cent. of cases examined. ("Fourth Annual Report of the Committee of Collect. Invest. Anat. Soc. Gt. Brit. and Ireland," Journ. Anat. and Physiol. vol. xxviii. p. 64) In place of being united to the third metacarpal, the styloid process may be fused with either the capitate bone or the lesser multangular, under which conditions the base of the third metacarpal bone is without this characteristic apophysis.
Phalanges. Several instances have been recorded of cases in which there were three phalanges in the thumb. Bifurcation of the terminal phalanges has occasionally been met with, and examples of suppression of a phalangeal segment or its absorption by another phalanx have also been described. (Hasselwander, Zeits. für Morph. u. Anthr. vol. vi. 1903.)
Hip Bone. Some of the anomalies met with in the hip bone are due to ossification of the ligaments connected with it; in other cases they depend on errors of development. Failure of union between the pubic and ischial rami has also been recorded. Cases have occurred where the obturator groove has been bridged across by bone, and one case is noted of absence of the acetabular notch on the acetabular margin. In rare cases the os acetabuli (see Ossification) remains as a separate bone. Derry (Journ. Anat. and Physiol. vol. xlv. p. 202) has drawn attention to the occurrence of a small accessory articular facet, situated on the rough non-articular area immediately behind the auricular surface of the ilium, which articulates with a depressed facet on the posterior surface of the sacrum to the lateral side of the first posterior sacral foramen, in the neighbourhood of the transverse process of the second sacral segment. This he homologises with the normal articulation between the ilium and sacral transverse processes found in many lower animals.
Femur.-Absence of the fovea on the head of the femur for the attachment of the ligamentum teres has been recorded. This corresponds with the condition met with in the orang. Not infrequently there is an extension of the articular surface of the head on to the anterior and apper aspect of the neck; this is pressure facet" caused by the contact of the iliac portion of the acetabular margin with the neck of the bone, when the limb is maintained for long periods in the flexed position, as in tailors, and also in those races who habitually squat (Lane, Journ. Anat. and Physiol. vol. xxii. p. 606).
The occurrence of a trochanter tertius has been already referred to. Its presence is not confined to individuals of powerful physique, but may occur in those of slender build, so far suggesting that it is not to be regarded merely as an indication of excessive muscular development. The observations of Dixon (Journ. Anat. and Physiol. vol. xxx. p. 502), who noted the occurrence of a separate epiphysis in three cases in connexion with it, seem to point to its possessing some morphological significance. Occasionally the gluteal tuberosity may be replaced by a hollow, the fossa hypotrochanterica, or in some cases the two may co-exist.
The angle of the neck is more open in the child than in the adult, and tends to be less when the femoral length is short and the pelvic width great-conditions which particularly appertain to the female. There is no evidence to show that after growth is completed any alteration takes place in the angle with advancing years (Humphry).
The curvature of the body may undergo considerable variations, and the appearance of the posterior surface of the bone may be modified by an absence of the linea aspera, a condition resembling that seen in apes; or by an unusual elevation of the bone which supports the ridge (fémur à pilastre), produced, as Manouvrier has suggested, by the excessive development of the muscles here attached.
Under the term "platymerie," Manouvrier describes an antero-posterior compression of the proximal part of the body, frequently met with in the femora of prehistoric races.
Patella.-Cases of congenital absence of the patella have been recorded.
F. C. Kempson (Journ. Anat. and Physiol. vol. xxxvi.) has recently drawn attention to the condition described as emargination of the patella. In specimens displaying this appearance the margin of the bones is concave from a point about half an inch to the lateral side of the middle line, to a point half-way down the lateral margin of the bone; here there is usually a pointed spine directed proximally and laterally. The condition appears to be associated with the insertion of the tendon of the vastus lateralis. G. Joachimstal (Archiv u. Atlas der normalen und pathologischen Anatomie in typischen Röntgenbildern, Bd. 8) figures a case in which on both sides the patella was double in an adult, the distal and much the smaller portion was embedded in the ligamentum patellæ.
Tibia.—The tibia is often unduly compressed from side to side, leading to an increase in its antero-posterior diameter as compared with its transverse width. This condition is more commonly met with in the bones of prehistoric and savage races than in modern Europeans. Attention was first directed to this particular form by Busk, who named the condition platyknemia. The general appearance of such tibiæ resembles that seen in the apes, and depends on an exceptional development of the tibialis posterior muscle, though, as Manouvrier has pointed out, in apes this is associated with the direct action of the muscle on the foot, as in climbing, whereas in man, as a consequence of the bipedal mode of progression, the muscle is employed in an inverse sense, viz., by steadying the tibia on the foot, and thus providing a fixed base on which the femur can move. This explanation, however, is disputed by Derry (Journ. Anat. and Phys. vol. xli. p. 123). Such platyknemic tibiæ are occasionally met with in the more highly civilised races, and are, according to Manouvrier, associated with habits of great activity among the inhabitants of rough and mountainous districts.
Another interesting condition is one in which the proximal extremity is more strongly recurved than is usual. This retroversion of the head of the tibia was at one time supposed to represent an intermediate condition in which the knee could not be fully extended so as to bring the axis of the leg in line with the thigh; but such opinion has now been upset by the researches of Manouvrier, who claims that it is the outcome of a habit not uncommon amongst peasants and countrymen, viz., that of walking habitually with the knees slightly bent.
Habitual posture also leaves its impress on the form of the tibia, and in races in which the use of the chair is unknown, the extreme degree of flexion of the knee and ankle necessitated by the adoption of the squatting position as an attitude of habitual rest is associated with an increase in the convexity of the lateral condylic surface, and the appearance, not infrequently, of a pressure facet on the anterior border of the distal extremity, which rests in that position on the neck of the talus. Cases of congenital absence of the tibia have been frequently described, amongst the most recent being those recorded by Clutton, Joachimsthal, Bland-Sutton, and Waitz.
Fibula. The fibula may be ridged and grooved in a remarkable manner, as is the case in many bones of prehistoric races. This is probably associated with a greater development and perhaps with more active use of the muscles attached to it.
The proximal articular facet varies much in size. Bennett (Dublin Journ. Med. Sc., Aug. 1891) records a case in which it was double, and also notes the occurrence of specimens in which it was absent and in which the head of the bone did not reach the lateral condyle of the tibia.
Many instances of partial or complete absence of the bone have been published. (Lefèbre, Contribution à l'étude de l'absence congénitale du péroné, Lille, 1895.)
Talus. The anterior calcanean facet is sometimes separated from the middle by a nonarticular furrow. The posterior process, often largely developed, is occasionally (2.6 per cent.) a separate ossicle forming what is known as the os trigonum (Bardeleben); or it may be united to the body of the talus by a distinct synchondrosis. A smooth articular surface may occasionally be found on the medial side of the proximal surface of the neck. This is a pressure facet dependent on the frequent use of the ankle-joint in a condition of extreme flexion, and is caused by the opposition of the bone against the anterior edge of the distal end of the tibia.
The form of the bone at birth differs from that of the adult in that the medial splay of the neck on the body is more pronounced, forming on an average an angle of 35° as compared with a mean of 12° in the adult; moreover, the articular surface for the medial malleolus extends forwards along the medial side of the neck, and to some extent overruns its superior surface. This is doubtless a consequence of the inverted position of the foot maintained by the foetus during intra-uterine life. In these respects the foetal bone conforms to the anthropoid type.
For a detailed study of the varieties of this bone, see R. B. S. Sewell. (Journ. Anat. and Physiol. vol. xxxviii.)
Calcaneus. The trochlear process is occasionally unduly prominent, constituting the submalleolar apophysis of Hyrtl, and cases are recorded of the calcaneus articulating with the navicular. (Morestin, H., Bull. de la Soc. Anat. de Paris, 1894, 5o sér. t. 8, n. 24, p. 798; and Petrini, Atti del XI. Congr. Med. Internaz. Roma, 1894, vol. ii., "Anat." p. 71.) Pfitzner (Morphologische Arbeiten, vol. vi. p. 245) also records the separation of the sustentaculum tali to form an Os sustentaculi. (See also P. P. Laidlaw, Journ. Anat. and Physiol. vol. xxxviii. p. 133.)
Navicular. According to Manners Smith this bone displays more variety of form than any other of the tarsal bones. He accounts for this both on morphological and mechanical grounds. He regards the tuberosity as probably of threefold origin, an apophysial, an epiphysial, and a sesamoid element, the latter being the so-called sesamoid bone in the tendon of the tibialis posterior. Cases are recorded where the tuberosity has formed an independent ossicle.
Cuneiform Bones.-Numerous cases of division of the first cuneiform bone into dorsal and plantar parts have been recorded; the frequent division of its metatarsal articular facet is no doubt correlated with this anomalous condition. T. Dwight has described (Anat. Anz. vol. xx. p. 465) in two instances the occurrence of an os intercuneiforme. The ossicle so named lies on the dorsum of the foot at the posterior end of the line of articulation between the first and second cuneiform bones.
Cuboid. Blandin has recorded a case of division of the cuboid. Occasionally there is a facet on the lateral surface of the bone for articulation with the tuberosity of the fifth metatarsal (Manners Smith).
Tarsus as a Whole.-Increase in the number of the tarsal elements may be due to the occurrence of division of either the first cuneiform or the cuboid bone, or to the occasional presence of an os trigonum. Cases of separation of the tuberosity of the navicular bone have been recorded, and instances of supernumerary ossicles between the first cuneiform and second metatarsal bone have been noted. Stieda mentions the occurrence of a small ossicle in connexion with the articular surface on the anterior and upper part of the calcaneus, and Pfitzner notes the occurrence of an os sustentaculi. For further information on the variations of the skeleton of the foot, see Pfitzner. (Morphologische Arbeiten, vol. vi. p. 245.)
The possibility of an injury having been the cause of the occurrence of some of these so-called supernumerary ossicles must not be overlooked. The use of the Röntgen rays has proved that accidents of this kind are much more frequent than was at first supposed.
The reduction in the number of the tarsus is due to the osseous union of adjacent bones. In many instances this is undoubtedly pathological, but cases have been noticed (Leboucq) of fusion of the cartilaginous elements of the calcaneus and talus, and the calcaneus and navicular in fœtuses of the third month.
Metatarsal Bones.-Several instances of separation of the tuberosity of the fifth metatarsal (os Vesaleanum) have been recorded, whilst numerous examples of an os intermetatarsum between the bases of the first and second metatarsal bones have been recorded by Gruber and others. The tubercle on the base of the first metatarsal for the attachment of the peronæus longus tendon is occasionally met with as a separate ossicle. An epiphysis over the spot where the tuberosity of the fifth metatarsal rests on the ground has been described. (Kirchner, Archiv klin. Chir. B 80.)
Phalanges. It is not uncommon to meet with fusion of the second and third phalanges, particularly in the fifth, less frequently in the fourth, and occasionally in the second and third toes. The union of the phalangeal elements has been observed in the foetus as well as the adult (Pfitzner). The proportionate length of the phalanges varies much; in some cases the ungual phalanges are of fair size, the bones of the second row being mere nodules, whilst in other instances the reduction in size of the terminal phalanges is most marked.
SERIAL HOMOLOGIES OF THE VERTEBRÆ.
It is a self-evident fact that the vertebral column consists of a number of segments or vertebræ all possessing some characters in common. These vertebræ or segments undergo modifications
according to the region they occupy and the functions they are called upon to serve, so that their correspondence and identity is thereby obscured. There is no difficulty in recognising the homology of the bodies and vertebral VERSE PROCESS arches throughout the column.
According to some anatomists the vertebral arch is the more primitive element in the formation of a vertebra, whilst others hold that the bodies are the foundation of the column. Be that as it may, we find that in the higher vertebrates, at least, the bodies are the parts which most persist. They are, however, TRANSVERSE Subject to modifications dependent on their fusion with one another. This occurs in the cervical part of the column where the body of the first cervical or atlas has for functional reasons become fused with the body of the second or epistropheus to form the dens of that segment. For similar reasons, and in association with the union of the girdle of the hind-limb with the column, the bodies of the vertebræ which correspond to the sacral segment become fused together to form a solid mass. In the terminal portion of the caudal region the bodies alone represent the vertebral seg
As regards the vertebral arch, this in man becomes deficient in the lower sacral region, and absent altogether in the lower TRANSVERSE Coccygeal segments. The
spinous processes are absent in the case of the first cervical, lower sacral, and all the coccygeal vertebræ, and display characteristic differences in the cervical, thoracic, and lumbar regions, which have been already described. The articular processes (zygapophyses) are secondary developments, and display great diversity of form, determined by their functional requirements. It is noteworthy that, in the case of the upper two cervical vertebræ, they are so disposed as to lie in front of the foramina of exit of the upper two spinal nerves, and by this arrangement the weight of the head is transmitted to the solid column formed by the vertebral bodies, and not on to the series of vertebral arches. It is in regard to the homology of the transverse processes, so called, that most difficulty arises. In the
COSTAL ELEMENT (RIB)
FIG. 280.-DIAGRAM TO ILLUSTRATE THE HOMOLOGOUS PARTS OF THE VERTEBRÆ. The bodies are coloured purple; the vertebral arch and its processes, red; the costal elements, blue. A, from above. B, from the side.
thoracic region they can best be studied in their simplest form; here the ribs-which Gegenbauer regards as a differentiation from the inferior or hæmal arches, in opposition to the view advanced by others that they are a secondary development from the fibrous intermuscular septa-articulate with the transverse processes and bodies of the thoracic vertebræ through the agency of the tubercular (diapophyses) and capitular (parapophyses) processes respectively, the latter being placed, strictly speaking, on the vertebral arch behind the line of the neuro-central synchondrosis.
An interval is thus left between the neck of the rib and the front of the transverse process ; this forms an arterial passage which corresponds to the foramen transversarium in the transverse processes of the cervical vertebræ, the anterior bar of which is homologous with the head and tubercle of the thoracic rib, whilst the posterior part lies in series with the thoracic transverse process. These homologies are further emphasised by the fact that in the case of the seventh cervical vertebra the anterior limb of the so-called transverse process is developed from an independent ossific centre, which occasionally persists in an independent form as a cervical rib.
In the lumbar region the lateral or transverse process is serially homologous with the thoracic ribs, though here, owing to the coalescence of the contiguous parts, there is no arterial channel between the rib element and the true transverse process, which is represented by the accessory processes (anapophyses), placed posteriorly at the root of the so-called transverse process of human anatomy. Support is given to this view by the presence of a distinct costal element in connexion with the transverse process of the first lumbar vertebra, which accounts for the occasional formation of a supernumerary rib in this region. The cases of foramina in the transverse processes of the lumbar vertebræ (see p. 275) are also noteworthy as supporting this view.
In the sacrum the lateral part of the bone is made up of combined transverse and costal elements, with only very exceptionally an intervening arterial channel. In the case of the upper three sacral segments the costal elements are largely developed and assist in supporting the ilia, and they are called the true sacral vertebræ; whilst the lower sacral segments, which are not in contact with the ilia, are referred to as the pseudo-sacral vertebræ.
The anterior arch of the atlas vertebra is, according to Froriep, developed from a hypochordal strip of cartilage (hypochordal spange).
MEASUREMENTS AND INDICES EMPLOYED IN PHYSICAL ANTHROPOLOGY.
The various groups of mankind display in their physical attributes certain features which are more or less characteristic of the stock to which they belong. Craniology deals with these differences so far as they affect the skull. The method whereby these differences are recorded involves the accurate measurement of the skull in most of its details. Such procedure is included under the term craniometry. Here only the outlines of the subject are briefly referred to; for such as desire fuller information on the subject, the works of Broca, Topinard, Flower, and Turner may be consulted.
The races of man display great variations in regard to the size of the skull. Apart altogether from individual differences and the proportion of head-size to body-height, it may be generally assumed that the size of the skull in the more highly civilised races is much in excess of that displayed in lower types. The size of the head is intimately correlated with the development of the brain. By measuring the capacity of that part of the skull occupied by the encephalon, we are enabled to form some estimate of the size of the brain. The cranial capacity is determined by filling the cranial cavity with some suitable material and then taking the cubage of its contents. Various methods are employed, each of which has its advantage. The use of fluids, which of course would be the most accurate, is rendered impracticable, without special precautions, owing to the fact that the macerated skull is pierced by so many foramina. As a matter of practice, it is found that leaden shot, glass beads, or seeds of various sorts are the most serviceable. The results obtained display a considerable range of variation. For purposes of classification and comparison, skulls are grouped according to their cranial capacity into the following varieties:
Microcephalic skulls are those with a capacity below 1350 c.c., and include such well-known
varieties: American Indians, Chinese, some African Negroes.
Megacephalic skulls are those with a capacity over 1450 c.c., and are most commonly met with in the more highly civilised races: Mixed Europeans, Japanese, etc.
Apart from its size, the form of the cranium has been regarded as an important factor in the classification of skulls; though whether these differences in shape have not been unduly emphasised in the past is open to question.
The relation of the breadth to the length of the skull is expressed by means of the cephalic index which records the proportion of the maximum breadth to the maximum length of the skull, assuming the latter equal 100, or
Max. breadth × 100
- Cephalic index.