Page:Encyclopædia Britannica, Ninth Edition, v. 2.djvu/174

160 APE proportion borne by this region of the spine to all the more anterior parts is greatest in Ateles, almost three to one; in the other longest-tailed genera it is rarely so large as two to one. The absolute length of the tail is greatest in the Semnopithecince, where also the individual caudal vertebrae attain their greatest length, namely, two inches. The caudal vertebrae generally increase in length as we proceed backwards from the sacrum, till about the seventh, eighth, or ninth, which, with the tenth and eleventh, are the longest caudal vertebrae in most long-tailed forms. In Ateles, however, it is the eleventh, twelfth, thirteenth, and fourteenth vertebras that are the longest. In the Simiince and in Inuus the caudal vertebrae decrease in length as we proceed backwards. Except in the forms just named, all the first four caudal vertebree possess a complete neural arch, sometimes six are so provided, but only in Ateles does the number attain eight. "With the same exceptions, again, the first four caudal vertebrae unite by articular processes, while transverse processes (single or antero-posteriorly PIG. 18. Skeleton of Chacma Baboon (Cynocephalus porcariia). From De Blainville. double) exist in a great part of the tail. In Ateles the caudal vertebrae are (as might be expected from the very prehensile character of the tail) exceptionally provided with bony processes serving as points of muscular attachment. Chevron bones and processes for their attachment are altogether want ing only in the Simiince and in Macacus inuus. They attain their maximum in Ateles, where they present almost every variety of development in one or other part of the caudal region. Certain vertebral processes, which in man are generally inconspicuous, and which are but little developed in the Simiince, attain in lower forms a marked development. These are the metapophyses and anapophyses. The first of these generally appear about the eighth or ninth dorsal vertebra, and may thence be traced backwards into the anterior caudal vertebrae, where they end by coalescing with the prezygopophyses. In Ateles these processes may sometimes be traced as far forward as the third cervical vertebra. The anapophyses become, below the Simiince, very conspicuous, projecting outwards and backwards from one vertebra, and embracing the prezygopophysis of the vertebra next behind. Generally they may be traced from the eighth or ninth dorsal vertebra to the penultimate lumbar vertebra. They attain their maximum of relative size in the lower Cebidce. They may (as sometimes in Ateles and Cynocephalus) be traced on to the posterior cervical vertebrae, while they appear to coalesce with the transverse processes in the tail, and thus they may be developed almost throughout the vertebral column. The Cebidce often develop hyperapophyses in the last dorsal and in the lumbar vertebrae. These processes are some what similar to ancijiophyses, but are placed much higher, and each pair embraces the spinous process of the vertebra next behind. In most apes the sternum is quite narrow, and consists of a more or less enlarged manubrium, followed by a chain of sub-equal and antero-posteriorly elongated bones from three to six in number. In the Simiince alone do we find a broad sternum, or one consisting of a manubrium, followed by one bone only, as in Hylobates. The orang presents a singular peculiarity, in that the breast-bone long remains made up of ossifications arranged in pairs, side by side, successively. The total number of ribs has already been indicated in speaking of the dorsal vertebrae. The true ribs are seven in number on each side in the highest forms, but in Hylobates there are some times eight. In Ateles there are sometimes nine pairs. In Hapale the number varies from six to eight, and it is seven or eight in the other genera. The " angles " of the ribs are never so marked as in man. They are most marked in Hylolates. Pithecia is distinguished by the greater relative breadth of the ribs. In no ape is the thorax half as broad again as it is deep from back to breast. Never theless, in the Simiince, its transverse diameter exceeds its depth by from about one-fourth to a little under one-third of the latter. In Ateles (and sometimes also in Mycetes) the thorax is wider than it is deep, but in all the rest it is narrow, being deeper than it is wide. The Append icular 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 tho 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 nearest approximation being made by Nycti- pithccus and Callithrix, namely, about 137 to 100. The length of the foot, compared with that of the hand, is exceptionally small in the Simiince, namely, from 84 up to 115 to 100. 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 Cebidce, thus in Chrysothrix and Hapale it is less than 84 to 100. Only in the Simiince and in Ateles is the pectoral limb, without the hand, shorter than the spine. The scapula of the gorilla presents a remarkable likeness to that of man, but that of its congener, the chimpanzee (the posterior vertebral angle being so acute), is less like man s than is that of the orang. The size of the supra- spinous fossa, as compared with the inf ra-spinous one, attains its maximum in the gorilla and Mycetes. In Simia and the Pitheciince 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 Simiince (except Ateles and Pithecia), and attains its maximum of convexity in aged Cynocephali. A supra- scapular notch is not well defined in the great majority of the Simiadce, but in some of the Cebidce (Ateles and Mycetes) it is constantly, and in others often, so enclosed as to become a foramen. In Mycetes a remarkable flat pro cess springs from the bridge of bone encircling this foramen. This process exists in no other genus. The surface for the teres major muscle projects out very strongly in the Cyno

pithednce and in Cebus and Chrysothrix. The acromion