1902 Encyclopedia > Ape > Ape Skeleton - Appendicular Skeleton: Introduction; Scapula; Clavicle; Humerus.

(Part 19)

(C) The Anatomy of Apes (cont.)

Ape Skeleton - Appendicular Skeleton: Introduction; Scapula; Clavicle; Humerus.

The Appendicular Skeleton --
The development of this part of the skeleton has been indicated in a general manner in speaking of the external form. The length of the pelvic limb compared with the pectoral one -- the foot and hand being removed -- attains in no ape the proportion that it does in man, i.e., 145 to 100; the neatest approximation being made by Nyctipithecus and Callithrix, namely, about 137 to 100. the length of the foot, compared with that of the hand, is exceptionally small in the Simiinae, namely, from 84 up to 115 to 1000. its greatest relative length is in Chrysothrix, viz.,about 177 to 100. in man it is about 134 to 100. the entire pectoral limb (measured from the summit of the head of the humerus to the distal end of the longest digit) is absolutely longest in the gorilla and orang. Its proportion to the spine is greatest in Hylobates, where it may attain the proportion of 222 to 100. Next come Ateles 174, Simia 170, the gorilla 150, and the chimpanzee 152. The rest vary from 121 to a little shorter than the spine, except certain of the lower Cebidae, thus in Chrysothrix and Hapale it is less then 84to 100. Only in the Simiinae and in Ateles is the pectoral limb, without the hand, shorter than the spine.

Skeleton of the Gorilla Image

Fig. 19 -- Skeleton of the Gorilla (Troglodytes gorilla). From De Blainville.

The scapula of the gorilla present a remarkable likeness to that of man, but that of its congener, the chaimpanzee (the posterior vertebral angle being so acute), is less like man's than is that of the orang. The size of the supraspinous fossa, as compared with the infra-spinous one, attains, its maximum in the gorilla and Mycetes. In Simia and the Pitheciinae the supra-spinous fossa is exceptionally small. The margin, corresponding with the superior margin of man's scapula, is generally convex in the forms below the Simiinae (except Ateles and Pithecia), and attains its maximum of convexity in aged Cynocephali. A suprascapular notch is not well defined in the great majority of the Simiadae, but in some of the Cebidae (Ateles and Mycetes) it is constantly, and in other often, so enclosed as to become a foramen. In Mycetes a remarkable flat process springs from the bridge of bone encircling this foramen. This process exists in no other genus. The surface for the teres major musvcle projects out very strongly in the Cynopithecinae and in Cebus and Chrysothrix. The acromion and coracoid processes are short in the lower Simiadae; both are long in the Simiadae and in Ateles.

The clavicle is well developed in every species of the order, and that of the orang is absolutely the largest; and it is longest, compared with the spine, in that animal and in Hylobates, being as 28 or 32 to 100, while in the lower Cebidae it may be less than 12 to 100. This bone is exceptionally slender in Mycetes, and is broadest in Troglodytes and the Cynopithecinae. In the lower Simiadae a fossa is excavated beneath the arcomial end of the bone. Rarely, as in Simia, there is a very prominent deltoidal ridge.

The humerus presents in all apes the same fossae and prominences as in man. Its length, as compared with the spine, is in Hylobates 70 or 80 to 100; but in most apes its length, thus compared, is between 45 and 30 to 100. The articular surface of the head is directed backwards and inwards, instead of almost exclusively inwards, as in man. In this respect man is most resembled by the Simiinae. The tuberosities may project upwards slightly above the articular head, as in Cynocephalus. General they are about on a level with its top, but may be decidedly below it, as in Ateles, Hylobates, and Simia. The radial border of the bicipital groove may be very prominent, as in Cynocephalus. The groove may be spanned by a bridge of bone, as sometimes in the chimpanzee. The position of the nutrients foramen varies even in different individuals. The supinator ridge is especially developed in Cynocephalus, Cebus, and Hapale. In the Simiinae it is only slightly developed. The external condyle is distinct in the Simiinae; in the other genera it is closely applied to the capitellum. A supra-condyloid foramen is never present normally in the Simiadae, but is present or less constantly in the Cebidae, from Cebus downwards, being perhaps most frequently absent in Hapale. Through this canal the brachial artery and median nerve pass. The projection of the radial margin of the trochlea is most prominent in the Simiinoe and Hapale. It almost disappears in the Cynopithecinae. The radius and ulna are never ankylosed together in apes. They diverge most, medianly, one from another in the gorilla. The radius is four-fifths the length of the spine in Hylobates, and three-fifths in Simia and Ateles. Mostly it is between three-tenths and two-fifths of the length of the spine, but may, as in Hapale, be only a quarter. The total length of the radius rather more frequently falls short of, than exceeds, that of the humerus. It exceeds it in Simia, Hylobates, Ateles, Cynocephalus, and sometimes in the Semnopithecinae. In all the others it falls short -- in none, however, so much so as in man, Brachyurus approximating most to the human proportion. The radius is stoutest in Cynocephalus, slenderest in Ateles, and, above all, in Hylobates. The ulna varies, like the radius, in length and breadth. The olecranon is broad in the Simiinae, but in the lower apes it is relatively larger, especially in Cynocephalus and Mycetes. The styloid process is very long in Hylobates, where it developed a prominence, on its hinder side, for the internal lateral ligament of the wrist. In Ateles this process is extremely long, having, as it were, a rounded articular head placed at the end of peduncle. The ulna articulates with the carpus in all the apes except Troglodytes and Simia.

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