So we see, in these animals, a marked and evident degeneracy of pelvic structure, allying them much more closely to the quadrupeds, especially to the Carnivora, than to mankind. And we may remark, more especially, that their fitness for the halaitual erect position is much dirainished by the want of direct antero-pos terior extension of the pelvis, produced by the flatness of the sacrum and the less marked sacro-vertebral angle, and the shortness and change of direction of the pubis; which renders the arms of the pelvic lever shorter from the cotyloid fulcrum, and the hold of the extensor and flexor muscles of the thigh less powerful in maintaining the standing posture. And, cor responding to this, we see in these animals. great diminution in the bulk of these muscles, particularly in the glutei and gastrocnemii, the plumpness of which constitute the buttocks and calves characteristic of the human figure From this cause, the gait of these animals in bipedal progression is very unsteady.
The expanded, everted, and large ischial tuberosities, and the strength of the ischio sacral arch, indicate that the sitting posture is more natural to the Simial race ; while the greater depth of the posterior than the supe rior part of the cotyloid brim shows, as well as the marked ilio-pubic angle, a provision for femoral support in a serniflexed, rather than an extended position. In the erect posture, from the flatness of the pelvis, the ischial tuberosi ties are brought close upon the femurs, and reach nearly half-way down their short shafts, interfering much with their motion.
According to Grant and \Vaguer, there is no cotyloid notch nor ligamentum teres in the Orangs ; but the cotyloid notch is present, though small, in the skeletons I have examined.
In the Hylobatis Lar, or long-armed Gibbon, the iTusc wings are flatter, and directed still more antero-posteriorly, crest rounded, large, and elevated ; ischia short, in a right line with the ilia, with flattened and expanded tube rosities, spines more distinctly marked, and rami directed, like the elongated pubes, more directly inwards. The cotyloid cavities are thus more widely separated, and the superior pelvic outlet has a triangular form, with the small end directed backwards. The sacrum is narrow and flat, forming a large angle with the spine, and composed of five vertebrze, of which the three upper, considered by Blainville to be the only true sacral vertebrm, articulate with the ilia. The coccyx, consisting, ac cording to Blainville, of seven, according to others, of five vertebrm, is short, there being no tail. The inferior outlet is large, and the true pelvis shallow, from the shortness and expansion of ischia.
The subgenera Callithrix, Cercocebua, and Semnopithecus present an elongation of the coccyx into a caudal appendage with prehensile attributes, and perforated for the continuation of the spinal cord, which widens still more the progressive separation from the human type. In the Squirrel Monkey are three sacral bones, of which the two upper articulate with the ilia, and the broad transverse processes of the last project towards the ischia, so as to give a square outline to the inferior outlet. Ischial tuberosities not flattened. In the Capuchin Monkey the ilia are parallel with the spine, the ischia are inclined forwards to the abdominal surface, and the pubes are more oblique. In the Senznopithecus entellus the sacrum is more arched laterally and broader. The ilia are prismatic and long, and project more behind the spinal column. The ischia and pubes are short, with flattened and expanded tuberosities, and no ischial spine. Ilio-pectineal eminence marked. In these tribes the posterior border of the elongated ilia is the thickest part of the bone, the anterior part being thinned and spread out more or less. The pubes are generally placed nearly at right angles to the ilia, and the lumbo-iliac angle is about 160°.
Of the genus Cercopithecus, or Baboon tribe, there is, in the brown Baboon, a well marked sacro-vertebral angle (155°) ; the two upper of the three sacral vertebrm only articulate with the ilia. The caudal vertebrm are not numerous. The ilia are more expanded, but still present the posterior concavity. The ischia are short, with very broad and flattened tuberosities. The pubes are flattened, with an acute superior border, and rostrated at the symphysis. Rio-pubic angle more marked (I10°). In the Mandrill, Papio Marnzon, the sacrum is more arched both vertically and transversely, and the promontory better marked. The coccygeal vertebrm are four in number, and there is no tail. The ilia are parallel with the spine, directly under which are placed the co tyloid cavities. The ischia are short, with much-expanded and flat tubers. The pubes are at right angles, both to ilia and spine, and the ischio-puhic symphysis is very little ad vanced before the plane of the spinal column.
In the Sapajous, or American Monkeys, there are three sacral vertebrm, of which the first only- articulates with the ilia in the Onistiii. In the White-bellied Ateles the ilia are longer and more expanded ; pubes more oblique ; ischia short, with no spine, and small tuberosities. In the Saimiri there is a very short ilio-ischium.