« PrécédentContinuer »
arrangement of fibres is evident, and the plantar surface of the neck of the talus is further strengthened by lamellæ arranged vertically.
In the separate bones the investing envelope is thin, though under the articular surfaces there is a greater density, due to the accession of lamella lying parallel to the articular planes. The stoutest bony tissue in the talus is met with in the region of the plantar surface of the neck, whilst in the calcaneus the greatest density occurs along the floor of the sinus tarsi.
The Metatarsus. In structure and the arrangement of their lamellæ the metatarsal bones agree with the metacarpus.
The Phalanges. In their general structure they resemble the bones of the fingers.
VARIATIONS IN THE SKELETON.
Cervical Vertebræ.-Szawlowski records the presence of an independent rib element in the transverse process of the fourth cervical vertebra. (Anat. Anz. Jena, vol. xx. p. 306.)
Atlas. The foramen transversarium is often deficient in front. Imperfect ossification occasionally leads to the anterior arch, and more frequently the posterior arch, being incomplete. The superior articular surfaces are occasionally partially or completely divided into anterior and posterior portions. In some instances the extremity of the transverse process has two tubercles. The transverse process may, in rare cases, articulate with a projecting process (paroccipital or paramastoid) from the under surface of the jugular process of the occipital bone (see p. 278). An upward extension from the medial part of the anterior arch, due probably to an ossification of the anterior occipito-atlantal ligament, may articulate with the anterior surface of the summit of the dens of the epistropheus. Allen has noticed the articulation of the superior border of the posterior arch with the posterior border of the foramen magnum. Cases of partial or complete fusion of the atlas with the occipital bone are not uncommon (see p. 278).
Epistropheus. In some instances the summit of the dens articulates with a prominent tubercle on the anterior border of the foramen magnum (third occipital condyle, see p. 278). Bennett (Trans. Path. Soc. Dublin, vol. vii.) records a case in which the dens was double. due to the persistence of the primitive condition in which it is developed from two centres, Occasionally the dens fails to be united with the body of the epistropheus, forming an os odontoideum comparable to that met with in the crocodilia. (Giacomini, Romiti, and Turner.) The foramen transversarium is not infrequently incomplete, owing to the imperfect ossification of the posterior root of the transverse process. Elliot Smith has recorded a case in which there was fusion between the atlas and epistropheus without any evidence of disease.
Seventh Cervical Vertebra.-The foramen transversarium may be absent on one or other side.
Thoracic Vertebræ.-Barclay Smith (Journ. Anat. and Physiol. Lond. 1902, p. 372) records five cases in which the superior articular processes of the twelfth thoracic vertebra displayed thoracic and lumbar characteristics on opposite sides. Duckworth (Journ. of Anat. and Physiol. vol. xlv. p. 65) has described a first thoracic vertebra, in which a bony process, arising from the front of the root of the transverse process, curves forwards and medially so as almost to enclose a foramen like that of the cervical vertebræ. The ventral surface of this process articulates with the neck of the first rib.
Lumbar Vertebra. The mamillary and accessory processes are sometimes unduly developed. The vertebral arch of the fifth lumbar vertebra is occasionally interrupted on either side by a synchondrosis which runs between the upper and lower articular processes. In macerated specimens the two parts of the bone are thus separate and independent. The anterior includes the body, together with the roots of the vertebral arches and the transverse and superior articular processes; the posterior comprises the inferior articular processes, the lamine, and the spine. (Turner, Challenger Reports, vol. xvi.) Fawcett has seen the same condition in the fourth lumbar vertebra. Szawlowski and Dwight record instances of the occurrence of a foramen in the transverse process of the fifth lumbar vertebra (Anat. Anz. Jena, vol. xx.), and Ramsay Smith describes a case in which the right transverse process of the fourth lumbar vertebra of an Australian sprang from the side of the body in front of the root of the vertebral arch, being unconnected either with the arch or articular process.
Sacrum. The number of sacral segments may be increased to six or reduced to four (see p. 276). Transition forms are occasionally met with in which the first sacral segment displays on one side purely sacral characters, .e. it articulates with the hip bone, whilst on the opposite side it may present all the features of a lumbar vertebra. Through deficiency in the development of the lamina, the sacral canal may be exposed throughout its entire length, or to a greater extent than is normally the case. (Paterson, Roy. Dublin Soc. Scientific Trans. vol. v. Series II.) Szawlowski and Barclay Smith record the occurrence of a foramen in the lateral part of the first sacral vertebra. (Journ. of Anat. and Physiol. Lond. vol. xxxvi. p. 372.) Vertebral Column as a Whole.-Increase in the number of vertebral segments is usually
due to differences in the number of the coccygeal vertebræ; these may vary from fourwhich may be regarded as the normal number-to six. The number of presacral or movable vertebræ is normally 24 (7 C, 12 Th, and 5 L); in which case the 25th vertebra forms the first sacral segment (vertebra fulcralis of Welcker). The number of presacral vertebræ may be increased by the intercalation of a segment either in the thoracic or lumbar region without any alteration in the number of the sacral or coccygeal elements: thus we may have 7 C, 13 Th, and 5 L, or 7 C, 12 Th, and 6 L, or it may be reduced by the disappearance of a vertebral segment -thus, 7 C, 12 Th, and 4 L. Such an arrangement presupposes developmental errors either of excess or default in the segmentation of the column. On the other hand, the total number of vertebral segments remaining the same (24 or 25), we may have variations in the number of those assigned to different regions due to the addition of a vertebral segment to one, and its consequent subtraction from another region. Thus, in the 24 presacral vertebræ, in cases of the occurrence of cervical ribs the formula is rearranged thus-6 Ĉ, 13 Th, and 5 L, or, in the case of a lumbar rib being present, the formula would be 7 C, 13 Th, 4 L, as happens normally in the gorilla and chimpanzee. Similarly, the number of the presacral vertebræ (24) may be increased by the withdrawal of a segment from the sacral region-7 C, 12 Th, 6 L, and 4 S-or diminished by an increase in the number of the sacral vertebræ, as in the formula 7 C, 12 Th, 4 L, and 6 S. Increase in the number of sacral segments may be due to fusion with a lumbar vertebra, or by the addition of a coccygeal element: the latter is more frequently the case. This variability in the constitution of the sacrum is necessarily correlated with a shifting tailwards and headwards of the pelvic girdle along the vertebral column. Rosenburg considers that the 26th, 27th, and 28th vertebræ are the primitive sacral segments, and that the sacral characters of the 25th vertebræ (the first sacral segment in the normal adult column) are only secondarily acquired. He thus supposes that during development there is a headward shifting of the sacrum and pelvic girdle, with a consequent reduction in the length of the presacral portion of the column. This view is opposed by Paterson (Roy. Dublin Soc. Scientific Trans. vol. v. Ser. II.), who found that ossification took place in the alæ of the 25th, vertebra (first adult sacral segment) before it made its appearance in the alæ of the 26th vertebra. He thus assumes that the alæ of the 25th vertebra may be regarded as the main and primary attachment with the ilium. His conclusions, based on a large number of observations, are at variance with Rosenburg's views, for, according to his opinion, liberation of the first sacral segment is more common than assimilation with the fifth lumbar vertebra, and assimilation of the first coccygeal vertebra with the sacrum is more common than liberation of the fifth sacral, thus leading to the inference that the sacrum tends to shift tailwards more often than headwards. Dwight (Anat. Anz. Jena, vol. xxviii. p. 33), after a study of this question, whilst admitting that some of these variations may be reversive, denies that there is any evidence that they are progressive, and further states that after the occurrence of the original error in development, there is a tendency for the vertebral column to assume as nearly as possible its normal disposition and proportions.
Sternum.-The sternum is liable to considerable individual variations affecting its length and direction. The majority of bones are asymmetrical, displaying irregularities in the levels of the clavicular facets. The higher costal facets may be closer together on one, usually the right side, than the other, whilst the synchondrosis sternalis is often oblique, sloping somewhat to the right. According to Birmingham, these are the result of the strain thrown on the shoulder by pressure either directly applied or through the pull of a weight carried in the hand.
Sometimes the sternum articulates with eight rib cartilages. This may happen on one or both sides, but when unilateral, much more frequently on the right side a condition by some associated with right-handedness. It is, however, more probably a persistence of the primitive condition of the cartilaginous sternum, in which each half is connected with the anterior extremities of the first eight costal arches. In some rare cases only six pairs of ribs articulate by means of their costal cartilages with the sternum. Recently Lickley has brought forward evidence to show that the seventh rib is undergoing regressive changes. (Anat. Anz. vol. xxiv. p. 326.)
Occasionally the presternum supports the first three ribs; in other words, the manubrium has absorbed the highest segment of the body. Keith has pointed out that this is the condition most commonly met with in the gibbon, and regards its occurrence in man as a reversion to the simian type. As far as is at present known, its occurrence seems more common in the lower races. Through errors of development the sternum may be fissured throughout, due to failure of fusion of the cartilaginous hemisterna. The two ossified halves are usually widely separated above, but united together below by an arthrodial joint. The heart and pericardium are thus uncovered by the bone. Occasionally this condition is associated with ectopia cordis, under which circumstances life is rendered impossible. Through defects in ossification the body of the sternum may be pierced by a hole, usually in its lower part, or through failure of fusion of the collateral centres one or more of the segments of the body may be divided longitudinally.
Sometimes small ossicles are found in the ligaments of the sterno-clavicular articulation. These are the so-called episternal bones, the morphological significance of which, however, has not yet been satisfactorily determined. They are by some regarded as the homologues of the interclavicle or episternal bone of monotremata, whilst by others they are considered to represent persistent and detached portions of the pre-coracoids.
Ribs. The number of ribs may be increased or diminished. Increase may occur by the addition of a cervical rib due to the independent development of the costal element in the transverse process of the seventh cervical vertebra. This may happen on one or both sides. The range of levelopment of these cervical ribs varies; they may unite in front with the sternum, or they may
be fused anteriorly with the cartilage of the first rib, or the cervical rib may be free. It may in some instances be represented mainly by a ligamentous band, or its vertebral and sternal ends may be alone developed, the intermediate part being fibrous. At times the vertebral end only may be formed, and may be fused with the first rib, thus leading to the formation of a bicipital rib such as occurs in many cetaceans. (For a detailed account of this anomaly see Wingate Tod's paper in the Journ. of Anat. and Physiol. vol. xlvi. pp. 244-288.) Increase in the number of ribs may also be due to the ossification of the costal element which is normally present in the embryo in connexion with the first lumbar vertebra. (Rosenberg, Morph. Jahrb. i.) Reduction in the number of ribs is less common. The twelfth rib rarely aborts; in some cases the first rib is rudimentary. Cases of congenital absence of some of the ribs have been recorded by Hutchinson, Murray, and Ludeke. Fusion of adjacent ribs may occur. (Lane, Guy's Hosp. Reports, 1883.) In this way, too, the occurrence of a bicipital rib is explained. This anomaly occurs most usually in connexion with the first rib, which either fuses with a cervical rib above or with the second rib below.
Variations in form may be in great part due to the occupation of the individual and the constricting influence of corsets. Independently of these influences, the ventral part of the body is sometimes cleft so as to appear double; at other times the cleft may be incomplete so as to form a perforation. Occasionally adjacent ribs are united towards their posterior part by processes having an intermediate ossicle between (Meckel), thus recalling the condition normally met with in birds; more usually, however, the bony projections are not in contact.
The number of true or vertebro-sternal ribs may be reduced to six, or increased to eight (vide ante, p. 276). Dwight (Journ. of Anat. and Physiol. vol. xlv. p. 438) describes a series of cases in which the interval between the transverse process of the first thoracic vertebra and the neck of the first rib is bridged across or converted into a linear cleft by a dorsal extension from the neck of the rib.
Costal Cartilages. Occasionally a costal cartilage is unduly broad, and may be pierced by a foramen. The number of costal cartilages connected with the sternum may be reduced to six or increased to eight (see p. 276). In advanced life there is a tendency towards ossification in the layers underlying the perichondrium, more particularly in the case of the first rib cartilage, in which it may be regarded as a more or less normal occurrence.
Frontal Bone. The variation most frequently met with is a persistence of the suture which unites the two halves of the bone in the infantile condition: skulls displaying this peculiarity are termed metopic. The researches of various observers-Broca, Ranke, Gruber, Manouvrier, Anoutchine, and Papillault (Rev. mens. de l'école d'Anthropol. de Paris, année 6, n. 3)-point to the more frequent occurrence of this metopic suture in the higher than in the lower races of man; and Calmette asserts its greater frequence in the brachycephalic than the dolichocephalic type, Separate ossicles (ossa suturarum) may occur in the region of the anterior fontanelle. The fusion of these with one or other half of the frontal explains how the metopic suture is not always in line with the sagittal suture (Stieda, Anat. Anz. 1897, p. 227); they occasionally persist, however, and form by their coalescence a bregmatic bone. (G. Zoja, Bull. Scientifico, xvii. p. 76, Pavia.) Turner (Challenger Reports, part xxix.) records an instance of direct articulation of the frontal with the frontal process of the maxilla in a Bush skull, and other examples of the same anomaly, which obtains normally in the skulls of the chimpanzee and gorilla, have been observed. (Journ. Anat. and Physiol. vol. xxiv. p. 349.)
There is sometimes a small arterial groove just medial to the supra-orbital notch or foramen, and occasionally the latter is double, the lateral aperture piercing the orbital margin wide of its middle point. Frequently the bone corresponding to the floor of the lacrimal fossa displays a cribriform appearance.
Schwalbe (1901) records the presence of small independent ossicles (supra-nasal bones) in the anterior part of the metopic suture. The same anatomist has also directed attention (Zeit. f. Morph. und Anthr. vol. iii. p. 93) to the existence of the metopic fontanelle, first described by Gerdy, and the occurrence of metopic ossicles (ossa interfrontalia) and canals.
Parietal. A number of cases have been recorded in which the parietal is divided into an upper and lower part by an antero-posterior suture parallel to the sagittal suture. Coraini (Atti d. XI. Congr. Med. Internaz. Roma, 1894, vol. v.) records a case in which the parietal was incompletely divided into an anterior and posterior part by a vertical suture. A tripartite condition of the bone has also been observed (Frasetto). The parietal foramina vary greatly in size, and to some extent in position. They are sometimes absent on one or other side, or both. They correspond in position to the sagittal fontanelle. Sometimes the ossification of this fontanelle is incomplete and a small transverse fissure remains. The parietal foramen represents the patent lateral extremity of this fissure after its edges have coalesced. Occasionally in the region of the anterior fontanelle an ossicle of variable size may be met with. This is the so-called pre-interparietal bone. According to its fusion with adjacent bones it may disturb the direction of the sagittal suture.
Occipital. The torus occipitalis transversus is the term applied to an occasional elevation of the bone which includes the external occipital protuberance and extends laterally along the superior curved line. Occasionally an emissary vein pierces the bone opposite the occipital protuberance. In about 15 per cent. of cases the hypoglossal canal is double. Much rarer three or even four foramina may be met with. The most striking of the many variations to which this bone is subject is the separation of the upper part of the squamous part of the occipital to form an independent bone-the interparietal bone, called also, from the frequency
of its occurrence in Peruvian skulls, the os Inca. By a reference to the account of the ossification of the bone, the occurrence of this anomaly is explained developmentally. place of forming a single bone the interparietal is occasionally met with in two symmetrical halves, and instances have been recorded of its occurrence in three or even four pieces. In the latter cases the two anterior parts form the pre-interparietals. Not uncommonly the internal occipital crest is split and furrowed close to the foramen magnum for the lodgment of the vermis of the cerebellum, and is hence called the vermiform fossa. Instances are recorded of the presence of a separate epiphysis between the basi-occipital and the sphenoid, the os basioticum (Albrecht) or the os pre-basi-occipitale. An oval pit, the fovea bursæ or pharyngeal fossa, is sometimes seen in front of the tuberculum pharyngeum. This marks the site of the bursa pharyngea. Occasionally the basilar part is pierced by a small venous canal. The articular surface of the condyles is sometimes divided into an anterior and posterior part. The so-called third occipital condyle is an outstanding process arising from the anterior border of the foramen magnum, the extremity of which articulates with the dens of the epistropheus. Guerri has recorded a case, in which in a foetal skull, there were two projecting tubercles in the position of the third occipital condyle, independent of the basi-occipital portions of the condyles. (Anat. Anz. vol. xix. p. 42.) This appears to confirm the view of Macalister that there are two different structures included under this name-one a medial ossification in the sheath of the notochord, and the second, a lateral, usually paired process, caused by the deficiency of the medial part of the hypochordal element of the hindmost occipital vertebra, with thickenings of the lateral parts of the arch. Springing from the under surface of the extremity of the jugular process, a rough or smooth elevated surface, or else a projecting process, the extremity of which may articulate with the transverse process of the atlas, is sometimes met with. This is the paroccipital or paramastoid process. The size and shape of the foramen magnum varies much in different individuals and races, as also the disposition of its plane. Elliot Smith has called attention to the asymmetry of the cerebral fossæ, which is correlated with asymmetry of the occipital poles of the cerebral hemispheres. Numerous instances of fusion of the atlas with the occipital bone have been recorded. Many are, no doubt, pathological in their origin; others are associated with errors in development. Interesting anomalies are those in which there is evidence of the intercalation of a new vertebral element between the atlas and occipital, constituting what is termed a pro-atlas.
Temporal Bone. The occurrence of a deficiency in the floor of the external acoustic meatus is not uncommon in the adult. It is met with commonly in the child till about the age of five, and is due to incomplete ossification of the tympanic plate. The line of the petro-squamosal suture is occasionally grooved for the lodgment of a sinus (petro-squamosal); sometimes the posterior end of this is continuous with a canal which pierces the superior border of the bone and opens into the transverse sinus. Anteriorly the groove may pass into a canal which pierces the root of the zygoma and appears externally above the lateral extremity of the petro-tympanic fissure. These are the remains of channels through which the blood passed in the foetal condition (see ante). Kazzander has recorded a case in which the squamous part of the temporal was pneumatic, the sinus reaching as high as the parietal and the squamoso-sphenoidal suture. Symington has described a case in which the squamous part was distinct and separate from the rest of the temporal bone in an adult; whilst Hyrtl has observed the division of the squamous part of the temporal into two by a transverse suture. The zygomatic process has been observed separated from the rest of the bone by a suture close to its root (Adacni). P. P. Laidlaw (Journ. Anat. and Physiol. vol. xxxvii. p. 364) describes a temporal bone in which there was absence of the internal acoustic meatus and of the stylo-mastoid foramen. The jugular fossa also was absent, and there was partial absence of the groove for the transverse sinus, associated with the presence of a large mastoid foramen. An instance of a rudimentary condition of the carotid canal is also referred to in the same volume by G. H. K. Macalister.
G. Caribbe (Anat. Anz. vol. xx. p. 81) notes the occurrence in idiots and imbeciles of a more pronounced form of post-glenoid tubercle, and associates it with regressive changes in the development of the temporal bone.
Sphenoid. Through imperfect ossification the foramen spinosum and foramen ovale are sometimes incomplete posteriorly. Le Double (Bull. et mém. de la Soc. d'Anth. de Paris, 5 sér. vol. iii. p. 550) records a case in which the foramen rotundum and the superior orbital fissure were united so as to form a single cleft.
Through deficiency of its lateral wall, the optic foramen, in rare instances, communicates with the superior orbital fissure. Duplication of the optic foramen is also recorded as a rare occurrence, the artery passing through one canal, the nerve through the other. Persistence of the cranio-pharyngeal canal is also occasionally met with. Owing to the ossification of fibrous bands which frequently connect the several bony points, anomalous foramina are frequently met with. Of such are the carotico-clinoid formed by the union of the anterior and middle clinoid processes, the pterygo-spinous foramen enclosed by the ossification of the ligament connecting the angular spine with the lateral pterygoid lamina, and the porus crotaphiticobuccinatorius similarly developed by the ossification of ligament immediately below and lateral to the inferior aperture of the foramen ovale.
Ethmoid. The size of the lamina papyracea is liable to considerable variations. In the lower races it tends to be narrower from above downwards than in the higher, in this respect resembling the condition met with in the anthropoids. The lamina papyracea may fail to articulate with the lacrimal owing to the union of the frontal with the frontal process of the maxilla
in front of it. (Orbito-maxillary-frontal suture. A. Thomson, Journ. Anat. and Physiol. vol. xxiv. p. 349.) Division of the lamina papyracea by a vertical suture into an anterior and posterior part has been frequently recorded. The number of the concha may be increased from two to four, or may be reduced to one. (Report of Committee of Collect. Invest., Journ. Anat. and Physiol. vol. xxviii. p. 74.)
Maxillæ. Not infrequently there is a suture running vertically through the bar of bone which separates the infra-orbital foramen from the infra-orbital margin. Through imperfections in ossification, the infra-orbital canal may form an open groove along the floor of the orbit. Duckworth records four instances of a spinous process projecting inwards into the apertura piriformis from the lower part of the nasal notch. A case has been described (Fischel) in which there was complete absence of the premaxillæ, together with the incisor teeth.
A not uncommon anomaly is the occurrence of a rounded elongated ridge extending along the interpalatal or intermaxillary sutures on the under surface of the hard palate. This is called the torus palatinus, and is of interest because its presence has given rise to the assumption that it was due to a pathological growth. (See Stieda, Virchow's Festschrift, vol. i. p. 147.)
The sulcus lacrimalis may be constricted towards its centre.
A part of the maxillary sinus may be constricted off anteriorly and, owing to its relation to the naso-lacrimal duct, is called the recessus lacrimalis.
Underwood (Journ. Anat. and Physiol. vol. xliv. p. 359) records the occurrence of all but complete septa dividing the cavity of the maxillary sinus.
Zygomatic Bone.-Cases of division of the zygomatic bone by a horizontal suture have been recorded, as well as instances of its separation into two parts by a vertical suture. Owing to the supposed more frequent occurrence of this divided condition in Asiatics the zygomatic has been named the os Japonicum. Barclay Smith (“ Proc. Anat. Soc.,” Journ. Anat. and Physiol., April 1898, p. 40) describes a case in which the zygomatic bone was divided into two parts, an upper and lower, by a backward extension of the maxilla, which articulated with the zygomatic process of the temporal, thus forming a temporo-maxillary arch. Varieties of a like kind have also been described by Gruber and others. Cases have been noted where, owing to deficiency in the development of the zygomatic, the continuity of the zygomatic arch has been incomplete.
Nasal Bones.-The size and configuration of the nasal bones vary greatly in different races, being, as a rule, large and prominent in the white races, and flat and reduced in size, as well as depressed, in the Mongolian and Negro stock. Complete absence of the nasal bones has been recorded, and their division into two or more parts has also been noted. Obliteration of the internasal suture is unusual; it is stated to occur more frequently in negroes, and is the recognised condition in adult apes.
Duckworth has recorded a case (Journ. Anat. and Physiol. vol. xxxvi. p. 257) of undue extension downwards of the nasal bone, which may be perhaps accounted for on the supposition that the lower part is a persistent portion of the premaxilla.
Lacrimal. The lacrimal is occasionally absent. In some cases it is divided into two parts; in others replaced by a number of smaller ossicles. In rare instances the hamulus may extend forwards to reach the orbital margin, and so bear a share in the formation of the face, as in lemurs (Gegenbauer). In other instances the hamulus is much reduced in size. Occasionally the lacrimal is separated from the lamina papyracea of the ethmoid by a down-growth from the frontal, which articulates with the frontal process of the maxilla, as is the normal disposition in the gorilla and chimpanzee. (Turner, Challenger Reports, "Zoology," vol. x. Part IV. Plate I.; and A. Thomson, Journ. Anat. and Physiol., London, vol. xxiv. p. 349.)
Inferior Concha.-A case in which the inferior concha were absent has been recorded by Hyrtl.
Vomer. Owing to imperfect ossification there may be a deficiency in the bone, filled up during life by cartilage. The separation of the two lamella along the anterior border varies considerably, and instances are recorded where they were separated by a considerable cavity within the substance of the bone. Instances of an extension forwards of the sphenoidal air sinus into and separating the lamina of the bone have also been described. The spheno-vomerine canal is a minute opening behind the rostrum of the sphenoid, and between it and the alæ of the vomer, by which the nutrient artery enters the bone.
Palate Bones. The occurrence of a torus palatinus may be noted (see Variations of Maxilla). Mandible. Considerable differences are met with in the height of the coronoid process : usually its summit reaches the same level as the condyle, or slightly above it; occasionally, however, it rises to a much higher level; in other cases it is much reduced. These differences naturally react on the form of the mandibular notch. The projection of the mental protuberance is also liable to vary. Occasionally the mental foramen is double, and sometimes the mylo-hyoid groove is for a short distance converted into a canal. There is often a marked eversion of the angle of the mandible, which Dieulafe homologises with the angular apophysis met with in lemurs and carnivora.
Clavicle. The clavicles of women are more slender, less curved, and shorter than those of men. In the latter the bone is so inclined that its acromial end lies slightly higher or on the same level with the sternal end. In women the bone usually slopes a little downward and laterally. The more pronounced curves of some bones are probably associated with a more powerful development of the pectoral and deltoid muscles, a circumstance which also affords an explanation of the differences usually seen between the right and left bones, the habitual use of the right