ADAPTATION OF SKELETON TO ERECT ATTITUDE. 



145 



III. TABLE OP THE HOMOLOGOUS PAETS OF THE SCAPULA AND ILIUM (ACCOBDING 



TO FLOWEE). 



SCAPULA. 



Supraspinous fossa . . . 

 Infraspinous fossa 

 Subscapular fossa . 

 Spine and acromion . 

 Superior or coracoid border. 

 Axillary or glenoid border , 



Superior anglj 

 Inferior angle 



Primitive condition. 



Vertebral surface . 

 Preaxial surface . 

 Postaxial surface . 

 Preaxial border . 

 Postaxial border 

 External border . 

 Dorsal extremity 



ILIUM. 



Sacral surface. 

 Iliac fossa. 

 G-luteal surface. 

 Ilio-pectineal line. 

 Posterior or ischial border. 

 Anterior or cotyloid border. 

 Iliac crest. 



Posterior superior spine. 

 Anterior superior spine. 



ADAPTATION OF THE SKELETON TO THE ERECT ATTITUDE. 



The axial skeleton of man is, for the purposes of station and progression, raised more fully to 

 the vertical position than is the case in any other animal ; and along with this the lower limks 

 are extended in lines parallel to the axis of the trunk. The feet rest on the ground by the 

 contact of the heel and the heads of the metatarsal bones, the centre of gravity of the body 

 falling within the basis of support. For the maintenance of this attitude, the constant action 

 of the muscles passing over the ankle-joint is more immediately necessary. But at the knec- 

 and hip-joints it is mainly by the mechanism of the ligaments and other parts of the joints, and 

 less directly by muscular action, that the erect attitude is maintained, as will be more fully 

 shown in the description of the different articulations. 



There are. besides, many peculiarities in the construction of the body, and especially of 

 the skeleton, which are associated with the assumption of the erect posture, and although 

 many of them have been noticed in the description of the bones, it may still be useful to re- 

 capitulate the chief ones briefly in this place. 



It may first be remarked that the full development of these peculiarities belongs to the 

 adult condition. In the infant, while still unable to walk, the large proportional size of the 

 head, amounting to nearly a fifth of the whole body, the comparative straightness of the ver- 

 tebral column, or absence of the curves which characterise the spine of the adult, the short- 

 ness of the lower limbs, and incompleteness of their structure, all contribute to render the 

 assumption of the erect attitude by the child, for a time, difficult and insecure. Thus the 

 middle distance between the vertex of the head and the sole of the foot in an infant is situated 

 somewhat above the umbilicus, while in the adult it is generally at the upper border of the 

 pubis, or even lower, in some part of the symphysis. In the child also, from the large dimen- 

 sions of the head and upper part of the body, the centre of gravity is carried to a considerably 

 higher point than in the adult. 



The skull of man differs from that of other animals in being nearly balanced on the vertebral 

 column, the condyles of the occipital bone being brought forwards to near the middle of the 

 base by the comparative shortness of that part of the skull which lies in front of the foramen 

 magnum, and the projection backwards of that which lies behind it. In quadrupeds the skull 

 extends forwards from the extremity of the column, and is sustained by the elastic ligamentum 

 nuchae, represented in man by a comparatively feeble structure which passes between the ex- 

 ternal occipital protuberance, and the spinous processes of the cervical vertebras. Together 

 with this altered relation of the head to the spine, the plane of the foramen magnum, which 

 in quadrupeds is vertical, becomes in man horizontal, or even inclined somewhat upwards 

 anteriorly. 



The spinal column, by its pyramidal form, is fitted to sustain the weight which bears down 

 upon its lower part, and by means of its different curvatures possesses elasticity and strength 

 combined, and allows considerable range of motion to the trunk, without removal of the centre 

 of gravity from within its base. The strong and expanded sacrum, is the immediate means of 

 transferring the weight of the trunk to the hip-bones and lower limbs. 



The thorax in man is comparatively short, compressed in the sagittal direction, and ex- 

 panded transversely, whereby the centre of gravity is carried backwards, nearer to the spine. 



The pelvis is of peculiar breadth in man, presenting an upper and a lower arch which meet 

 at the hip- joints, and is so inclined that a vertical line descending from the centre of gravity 

 of the body is in a plane slightly behind the centres of motion of the hip-joints. The breadth 

 of the pelvis enables the balance to be more easily maintained in lateral movements of the 

 body by compensating inclinations of different parts to opposite sides of the basis of support, 

 and the long neck of the femur gives an advantageous insertion to the muscles by which the 



