are straight in all other animals, because the weight of the viscera is differently supported. Even in the orang-outang, the sacrum is flat and contracted, and continued, together with the os coccygis, in a straight line with the vertebral column. If the human sacrum and coccyx had been continued in a straight line with the spine, as those of the orang-outang and monkeys are, the innominata remaining as at present, they would have projected beyond those bones, so as to disable us from sitting The curve which they describe, in man only, obviates this inconvenience; and allows the pelvis to rest securely in the sitting attitude on the broad and strong ischiatic tuberosities.

The influence of this structure on the direction and functions of the vagina will be considered afterwards.

The distribution, size, and offices of the muscular masses correspond to the organic arrangements of the skeleton. The lateral and posterior surfaces of the pelvis give origin to the powerful glutei, of which the exterior (glutei magni), exceeding in size all other muscles in the body, and covered by a remarkable stratum of fat, form the buttocks, which, by their ample, fleshy, and convex protuberances, conceal the anus; and are accounted both by the classical authors in natural history, as ARISTOTLE and BUFFON, and by the greatest physiologists, as GALEN and HALLER, as the chief character by which man is distinguished from the buttockless simiæ. Les fesses," says the great historian of nature, "n'appartiennent qu'à l'espèce humaine." The final cause of this prerogative has been assigned by an anatomist. "Solus homo ex omnibus animalibus commode sedet, cui carnosæ et magnæ nates contigere, et pro substernaculo pulvinarique, tomento repleto, inserviunt, ut citra molestiam sedendo, cogitationibus rerum divinarum animum rectius applicare possit."*

The use of the glutei, however, is not confined solely to what the pious SPIGELIUS has imagined; viz., the forming a cushion on which the body may be softly supported, for the purposes of divine cogitation; but they are very important agents in extending the pelvis on the thighs, and maintaining it in that state in the erect position of the trunk. In standing on both feet, the glutei magni fix the pelvis firmly behind, and counteract the natural tendency to fall forwards, which the weight of the head, the usual position of the upper limbs in front of the body, and the prominence of the abdominal viscera, impress Spigelius de hum. Corp. Fab. p. 9.

upon the trunk. Hence, the bulk and power of these very muscles in the human subject afford a clear proof that man was designed for the attitude on two feet. The other two glutei are not essentially concerned in the attitude of standing on both feet; but they are the principal agents in supporting and balancing the trunk on one foot, by inclining the pelvis over the head of that thigh-bone, on which the body rests, so that the centre of gravity of the trunk may be in a line drawn through that lower extremity. In this case, their exertion counteracts the tendency of the trunk to fall on that side which is not supported. These muscles are employed in a similar manner in progression: the gluteus magnus balances the pelvis, while one leg is carried before the other, and brought to the ground; and the two others support the trunk laterally, while the limb of the opposite side is in the air.

The gluteus magnus, which is the largest muscle of the human body, is so small and insignificant in animals, that it may be almost said not to exist. F. CUVIER observes of the orang-outang, "les fesses étoient presque nulles, ainsi que les mollets." TYSON indeed asserts, of the chimpansé, that "our pygmie had buttock or nates, as we shall see in the myology, but not so much as in man."+ However, in his apparently accurate figure there is no trace of them.

The extensors of the knee are much stronger in the human subject than in other mammalia; as their two-fold operation of extending the leg on the thigh, and of bringing the thigh forwards on the leg, forms a very essential part in the human mode of progression. The flexors of the knee are, on the contrary, stronger in animals; and are inserted so much lower down in the tibia, even in the monkeys, than in the human subject, that the cord which they form, keeps the knee habitually bent, and almost prevents the perfect extension of the leg on the thigh. Where the thigh and leg thus form an angle, instead of being continued in a straight line, the support of the body on the hind legs must be very insecure.

The extensor muscles of the ankle-joint, and chiefly those which form the calf of the leg, are the principal agents in progression. Hence man is particularly characterized by the largeness of his calves; and no animal equals him in this respect.

Annales du Muséum, v. 16, p. 47. The correctness of this remark is fully verified by the orang-outang belonging to Mr. Abel. It has neither buttocks nor calves.

+ Anatomy of a Pygmie, p. 14.

By elevating the os calcis, they raise the whole body in the act of progression; and, by extending the leg on the foot, they counteract that tendency, which the weight of the body has to bend the leg in standing. The muscles of the calves lift the heels, and thereby elevate the whole body, which is supported on the astragalus the weight is thus maintained on the anterior part of the feet, and the individual is said to stand on tiptoes. If the foot of one side be lifted from the ground, and the opposite heel be raised by the calf of its own side, the whole body is then elevated by the muscles of one calf. When a person stands on tiptoe with a burden on the shoulders, or any other part of the trunk, the weight of this, as well as of the body, must be raised and supported by the muscles of the calf. In running, leaping, jumping in the air, dancing, &c., the projection of the body is accomplished by the same power.

ARISTOLE, and others after him, have justly observed that calves of the legs can be ascribed to man only.

The whole arrangement of the thorax corresponds to the erect attitude of man. It is flattened anteriorly, possesses a very broad sternum, is wide transversely, but shallow from before backwards. Its lateral width and inconsiderable depth from sternum to spine, not only throw the arms far apart, and thus give a more extensive range to their motions, but diminish that preponderance of the trunk towards the front, which, although it is unimportant in the horizontal, is very inconvenient in the erect attitude. Man is said to be the only animal, in which the transverse exceeds the antero-posterior diameter of the chest. Even in the simia satyrus the latter exceeds the former measurement.*

The human sternum is short, as well as broad; hence a large space is left between the front of the chest and the pelvis, unprovided with bony supports; the weight of the viscera, which are sufficiently guarded by the abdominal muscles, is securely sustained below by the ample pelvis.

Quadrupeds have a thorax compressed laterally, narrow and keelshaped on its sternal aspect, consequently deep from sternum to spine, but confined in the transverse dimension. This structure, with the absence of clavicles, allows the front legs to come near together, to fall perpendicularly under the front of the trunk, and support it with firmness and facility. Their sternum is long and narrow, the ribs advance nearer to the * Camper, Œuvres, i. p. 115.

crista of the os innominatum, and together with the sternum cover a large share of the abdomen, and support its viscera more effectually in the horizontal position of the trunk. For the same purpose too, the ribs in many cases are more numerous than in man; viz., thirty-two in the hyena, thirty-six in the horse, forty in the elephant, and forty-six in the unau (Bradypus didactylus.)

These, with other points, which cannot escape observation, when the skeleton of any rather long-legged quadruped is compared to that of man, show how unfit he is for the attitude on all fours, which in his case can never be otherwise than unsteady, irksome, and fatiguing in the highest degree.

The spine of man presents some important peculiarities resulting from his characteristic attitude. One of these is its very remarkable increase of size in the lumbar region; an augmentation corresponding to that of the superincumbent weight, and to the magnitude of the efforts which this part has to sustain. The immense bulk of the sacrum,* far exceeding, in proportion to the rest of the body, that of any animal, is referable to the same cause, to the mode in which this weight is transmitted to the hip-bones, and thence to the lower limbs, and to the peculiar construction of the pelvis. The waving line + of the column, arising from a series of alternate curves in opposite directions, is altogether peculiar to man; it allows a proper distribution of the weight with respect to the centre of gravity, the line of which carried through the entire trunk must fall within the space covered by the feet, or by one foot when we support the body on one only. As this line passes through all the curves, motion is allowed in the upper regions without impairing the general equilibrium.

The cervical vertebræ of the monkeys, including the satyrus and troglodytes,§ are remarkable for the length and prominence

* In the chimpansé, says Tyson, "the os sacrum was nothing so dilated and spread, as 'tis in man; but contracted and narrow, as 'tis in apes; and very remarkably different from the human skeleton." P. 69.

This is excellently represented in Albinus's plates of the skeleton; particularly in the side view, tab. iii. I refer to the original Leyden edition of this incomparable work; which, when the plates of the bones are added, constitutes the most accurate, useful, and splendid publication ever produced in anatomy. Its merits cannot be estimated from the English editions.

"Les vertèbres cervicales sont remarquables par la longueur extraordinaire des apophyses epineuses des six inférieures; mais surtout par celle du milieu." "Les apophyses paroissent avoir besoin de cette longueur dans l'orang, pour qu'il puisse tenir mieux sa tête en equilibre. Je ne connois aucun autre animal dont les apophyses epineuses des vertèbres cervicales soient aussi longues, excepté le philandre d'Amérique." Camper, Œuvres, 1. 126, pl. 2. fig. 3.

Tyson, p. 68.

of the spinous processes; a peculiarity probably connected with the support of the head, which preponderates in front in consequence of the elongation of the jaws and the retreat of the occipital condyles backwards.*

I have explained how the lower extremities afford a sufficient base of support and solid columns to sustain the trunk, and how the same point is secured by the organic arrangements of the latter. The breadth of the human pelvis forms an ample basis for the body, and a firm point of action for the abdominal and other muscles, enabling them quickly to rectify the position of the parts above. In all the digitated animals, the pelvis is so narrow, that the trunk resembles an inverted pyramid: there would be great difficulty in maintaining it in equilibrio, even if it were possible for the animal to assume the erect position. In those instances, where the pelvis is broader, as in the hoofed animals, the other conditions of the upright stature are absent. The bear, however, forms an exception to these observations, and may be taught to stand and walk erect, although the posture is manifestly irksome to the animal. When quadrupeds endeavour to support themselves on the hind extremities, as for the purpose of seizing any objects with the fore-feet, they rather sit down than assume the erect position; for they rest on the thighs, as well as on the feet, and this can only be done, where the forepart of the body is small, as in the simiæ, squirrel, &c. In other cases the animal is obliged to support itself by the fore-feet also, as in the dog, cat, &c.

CHAPTER III.

On the upper Extremities: Advantageous Construction of the Human Hand: Man is two-handed, the Monkey kind four-handed: on the natural Attitude and Gait of Monkeys.

A CURSORY survey of the upper limbs will be sufficient to convince us that they are entirely unsuited to the office of supporting the body, and as well calculated for the uses to which we put them, of seizing and holding objects, and thereby executing, besides all the processes of the arts, a thousand minute but most serviceable actions of constant recurrence.

There is a general resemblance of form throughout the upper and lower extremities: their principal divisions, the number and

* This_great_development of the cervical spines is most remarkable in the pongo, where the enormous bulk of the jaws corresponds to it. See Audebert, Hist, Nat. des Singes et Makis, fol. Planche Anatomique 2, fig. 5.