Natural History Review/Series 2/Volume 1/Number 4/On the Myology of the Orang Utang (Simia Morio)
Having had an opportunity of dissecting the muscles of an Orang Utang, and of comparing them with those of the Magot (Inuus Rhesus) and of the Cebus Capuchinus, I have put together the following remarks on their myology, in the hope of drawing general attention to some points which have usually been overlooked.
I shall endeavour to point out the variations existing in the different species of the Quadrumana, as illustrated by the above-mentioned species, and to show how much closer is the connexion between the myological structure of the Platyrrhine prehensile-tailed Cebus and the Magot, than that existing between the latter animal and the Orang; secondly, to furnish parallels between the recorded variations of the muscular system in man and the arrangement of the muscles in the Quadrumana; and thirdly, to show that the Quadrumana differ among themselves in those points in which they differ from man: the distribution of the Flexor Longus Hallucis and Pollicis, for instance, differing as widely in the Orang, from that found in the bulk of the Quadrumana, as it does from that which obtains in man.
Unfortunately, comparative anatomists have almost exclusively confined their investigations to the osteology and nervous system of the Bimana and Quadrumana; and, while they have frequently noticed the approach which the lower races of mankind make to the quadrumanous type in those parts of their organization, few or no inquiries have been made into the myology of these races, and consequently the abnormal variations here mentioned are exclusively obtained from civilized races.
In many of the wild races, the external form of the limbs differs slightly from that of the civilized ; and I think it may be fairly presumed that the structure of the muscles would not unfrequently present corresponding modifications.[1]
In the following remarks, I have first described each muscle as it appeared in the Orang, and I have then compared it with the accounts given of the corresponding muscle in the Magot, Cebus, and other Quadrumana, and, lastly, with any similar variations which I have found recorded as occurring in man.
The works to which most frequent reference is made are— Recherches d'Anatomie comparée sur le Chimpansée, par W. Vrolik; M. Duvernoy's Memoir on the Myology of the Gorilla and other Anthropomorphous Apes, Archives du Museum d'Histoire Naturelle, tom. viii.; Encyclopédie Anatomique, traduit d' Allemand par A. J. L. Jourdan, tom. iii.; Mr. J. Hallett's Paper in the Edinburgh Medical and Surgical Journal, 1847; Anatomie Comparée, Recueil de Planches du Myologie, dessinées par G. Cuvier; Prof. Owen, Proceedings of the Zoological Society, vol. i.
I have confined my remarks almost entirely to the muscles of the anterior and posterior extremities, as they are the most subject to variations in the various orders of the Mammalia.
The Orang was a young specimen, and its muscles were but feebly developed, forming a very strong contrast to those of the Magot, which was an old individual, and very muscular. The age of the Orang may perhaps account for some of the differences between my dissections and those of Prof. Owen and M. Duvernoy.
The Muscles of the Anterior Extremity.
The inferior portion of the Trapezius arose from ten dorsal vertebræ, and its fibres did not communicate with those of the Latissimus dorsi, as they do in the Chimpanzee.[2]
The Rhomboidei Major and Minor were fused together, as in the Chimpanzee: in the latter animal this muscle does not reach the occipital bone, but the Orang in this respect resembles the Inui and Cynocephali.
The Levator Scapulæ, called Trachelo-scapularis by Duvernoy,[3] is inserted into the four anterior cervical vertebræ. This muscle is described by Duvernoy as having one digitation inserted into the occipital bone, another fusing with the sterno-mastoid, and three others into the cervical vertebræ. In the Gorilla, he describes three distinct fascicles; one of which is inserted into the transverse process of the Atlas, the other into the second, third, fourth, and fifth cervical vertebræ. In the Magot, he describes it as I found it in this Orang.
The slip to the sterno-mastoid, which Duvernoy found in the Orang, occurs as an accidental variety in man, as is mentioned by Theile.[4]
The Clavio-trachélien, or Acromio-trachélien, arose from the clavicle alone, and was inserted into the inner side of the transverse process of the atlas. In the Gorilla, it has the same insertion, but it arises from the acromion.[5]
The Latissimus Dorsi possessed much the same origin as in man, but scarcely reached so far up the back. The fibres which arose from the dorsal vertebrae remained distinct, and did not interlace with those of the inferior portion of the muscle; and, as they curved round the lower margin of the Teres Major, they formed a distinct head, separated from the rest of the muscle by a septum of dense tissue, which was inserted partly into the external fascia of the arm, and partly into the humerus, together with the tendon of the Teres Major. The larger and inferior portion of the muscle passed on to be inserted by a broad tendon, which curved round the humerus, and was inserted into the inner surface of that bone an inch and a half below the bicipital groove. At the distance of an inch and a half from the point of insertion, a strong muscular slip, called by Duvernoy the Dorsoepitrochlien, is given off, which passes down along the inner side of the long head of the Triceps, to be inserted into the fascia of the arm and the olecranon process of the ulna.[6]
In the Gorilla, the Dorso-epitrochlien receives a small slip from the tendon common to the Biceps and the Coraco-brachialis (Duvernoy, l.c., p. 80.) In the Cebus, the tendon of the portion coming from the dorsal vertebrae is not inserted together with that of the Teres Major, but close to it This modification of the Latissimus Dorsi appears common to all the Quadrumana, and must greatly relieve the strain thrown on the muscles of the arm and shoulder by the weight of the body when the animal is climbing. Corresponding modifications will be found in the posterior extremities.
The Teres Major was proportionately a stronger muscle than in man, and its tendon was inserted over a space of one inch and three-eighths: this was partly caused by its receiving a slip, as before mentioned, from the Latissimus Dorsi.
The Teres Minor differed only in its mode of origin; arising between the long head of the Triceps and the Infra-Spinatus muscles from the inferior border of the scapula.
The acromial portion of the Deltoid was inserted separately into the humerus by a thin tendinous band, while the mass of the muscle was inserted into the deltoid tuberosity, which was situated lower down the arm than in man.
In the Magot, it was divided, as stated by Duvernoy, into three almost distinct portions, which he calls Claviculaire, Coracodienne, et Sous-epineuse.
The Pectoralis Major arose by three distinct heads; one coming from the clavicle, the other two from the sternum and intercostal cartilages. The upper sternal portion did not, in this instance, reach higher than the third rib. The lower sternal portion arose from the costal cartilages, the ensiform appendage, and the sternum: it received, opposite the fifth rib, some fibres from the external oblique. The muscle was inserted by a broad tendon, extending from the anatomical neck, 218 inches down the anterior border of that bone. The fibres of the clavicular portion form the lowest and those of the lower sternal portion, the upper part of the tendon, as in man.
In the Chimpanzee (Vrolik, l.c. p. 18), this muscle has only a single sternal and clavicular origin. And Prof. Owen[7] describes it as formed in the Orang of sterno-humeralis, costo-humeralis, and sterno-costo-humeralis portions—apparently, therefore, in his specimen, the clavicular portion was wanting; neither does Sandifort mention any clavicular portion in the adult dissected by him.
In the Magot, a thin muscular slip, distinct from the Pect. Major, and beneath it, was found, which arose from the lower ribs, and terminated in a thin membranous expansion, which appeared to be inserted partly into the aponeurosis of the arm, and partly into the intermuscular septum and the humerus.
In Man, it is by no means unfrequent to find the sternal portion divided into two or more parts; the arrangement met with in the Magot is described in the human subject by Theile;[8] and Mr. Hallett[9] mentions a very similar one as occurring in man.
The Pectoralis Minor presented the same appearance as in man; in the Gorilla, Duvernoy states that it is divided into two portions; one passing in front of, the other behind the laryngeal sac.
The two heads of the Biceps remained distinct until they reached the lower third of the humerus. Taking its origin by fleshy fibres alongside of the long head of the Biceps and the Coraco-brachialis, and receiving fibres from them, was a muscular slip, described as très mince in the Chimpanzee (Vrolik, 1. c.p. 19), which, after accompanying the long head of the Biceps for 212 inches, leaves it to be inserted into the humerus and intermuscular septum, immediately below the insertion of the Corecobrachialis, and alongside of the internal portion of the Triceps. This slip is not mentioned by Duvernoy as occurring in the Orang, but he found it in the Chimpanzee and Gorilla: in the latter, it joined the Dorso-epitrochlien. It did not occur in the Cebus or Magot, and Cuvier[10] has not figured it in any of his plates.
This slip is a frequent occurrence in the human subject, the Biceps being subject to many variations.
The Triceps differed from that of man only in having the long head of greater proportionate strength: it had a large insertion, covering a space of one inch and seven-eighths into the inner and lower edge of the scapula.
In examining the muscles which move the hand of the Orang, we find that, whilst the extensor muscles closely correspond with those of man, the flexor muscles are modified, in order to strengthen the hand for grasping, while the capability for varied and delicate movements must be impaired.
The Supinator Longus was large, its origin covering a space of 312 inches on the humerus, and some of its fibres appearing to interlace with those of the long head of the Triceps as it passed downwards.
The Extensor Carpi Radialis Longior arose from the external condyloid ridge of the humerus. The lower two-thirds of this muscle were tendinous: it was inserted into the radial side of the metacarpal bone of the index.
The Extensor Carpi Radialis Brevior was larger and stouter than the preceding muscle, and had a similar insertion into the metacarpal bone of the middle finger.
The Extensor Communis Digitorum presented almost exactly the same appearance as in man. In the Chimpanzee, according to Duvernoy, the portion for the index finger is distinct, from its origin.
The Extensor Minimi Digiti arose alongside of the Extensor Carpi Ulnaris from the ulna and intermuscular septum, passed through a distinct sheath of the annular ligament, and split into two tendons inserted into the ring and little fingers. In the Chimpanzee, it is inserted into the little finger only. The Gorilla has the tendon strongly connected with that of the Extensor Communis; the muscular portion seemed also to form part of the Extensor Communis. (Duvernoy, 1. c.p. 97.) In the Cebus, it formed part of the same muscular belly as the Extensor Communis, but soon separated from it, and was inserted as in the Orang. In the Magot, its origin, disposition, and insertion all resembled those in the Orang.
The Extensor Indicis, instead of being inserted only into the index, was flattened out, and inserted chiefly into the base of the metacarpal bone of the middle finger, sending a few fibres to those of the index and ring fingers. In two specimens dissected by Duvernoy, he found this muscle performing the office of an Extensor proprius of the middle finger only, and in another specimen it was inserted into both the index and middle fingers; see also Cuvier, l.c. pl. 17.
In the Gorilla, according to Duvernoy (p. 97), it goes to the index only, but it is very weak. In the Chimpanzee, according to Vrolik, the tendinous insertion is confined to the index, but the muscle at its origin appears to be fused with the common Extensor. In an Ateles I found it to terminate by two distinct tendons; one of which was inserted into the index and radial side of the middle finger, the other into the ulnar side of the middle and the ring finger. In the Cebus and Magot, the two tendons were inserted severally into the middle and index fingers.[11]
The extensor muscles in the human subject are very liable to variations, and the commonest resemble those arrangements found normally in the Quadrumana. Mr. Hallett says of the Extensor Minimi Digiti, "it is occasionally absent, being replaced by the Extensor Communis; more frequently split into two tendons, or two muscles even, going to the ring and little fingers." The sending off of a slip to join the tendon of Extensor Communis going to the ring finger is described by Vesalius.[12] Theile[13] mentions the same arrangement as Mr. Hallett. Mr. Hallett also describes a case in which the Extensor Indicis was divided into two distinct muscles, the tendon of one of them going to unite with the index branch of the common extensor, while the other went to the middle finger: this was the most complete irregularity met with, but many minor grades were noticed. Theile[14] mentions the tendon being double, a branch going to the middle finger.[15]
The want of specialization of this muscle in the Orang must be regarded as a lower organization than that of the Chimpanzee or Gorilla, which, from their myology, I should think are able to point with their finger in the same manner as man.
The Pronator Teres, Flexor Carpi Radialis, Palmaris Longus, and Flexor Carpi Unaris presented the closest resemblance to the same muscles in man. But the individuality of the several muscles was less marked; they appeared to have a common origin from the inner condyle of the humerus and intermuscular septum, and owing to the interlacement of their fibres, none of the muscles could be traced out to their individual origins. The same remarks apply to these muscles in the Magot and Cebus.
The Flexor Sublimis Digitorum. The portion of this muscle which supplies the little finger left the rest of the belly, and became tendinous 212 inches above the origin of the other tendons.
The Flexor Profundus arose as in man, but had no tendon going to the index finger; as it passed through the annular ligament, the tendon of the middle finger received a slip from the tendon of the Flexor Longus Pollicis (Indicis), and gave one to that of the ring finger; the tendon of the ring finger sent no slip to that of the little finger, but the tendons supplying these fingers arose from the same fascicle of the muscle. In the Grorilla, the index tendon is wanting; and in both the Cebus and Magot the Flexor Profundus and Flexor Longus Pollicis are intimately connected in the palm.
(To be concluded in the next number.)
- ↑ Mr. Simpson noticed an undue shortness of the thumbs in the western Eskimos, and the absence of calf and flatness of the thighs has been often noticed in wild races by travellers.
- ↑ Rech. d'Anat. Comp. sur le Chimpansée, par W. Vrolik, p. 17.
- ↑ Duvernoy, Archives du Museum d'Histoire Naturelle, tom. viii. p. 74.
- ↑ Encyclopédie Anatomique, traduit d'Allemand par A. J. L. Jourdan, tom. iii. p. 124.
- ↑ This, the Acromio-basilar muscle of Vicq. d'Azyr, is eminently characteristic of the lower Mammalia; so that M. Duvernoy (second edition of Cuvier's Leçons, tome i. p. 371) even says, "On le trouve dans tous les mammifères, l'homme excepté, ce qui semblerait prouver qu'il est une des conditions de la station quadrupède." Its upper attachment varies in the Mammalian series from the lower cervical vertebræ (camel) to the occipital bone (rabbit). The human muscular variety, which appears to make the newest approach to the development of this muscle, is that observed by R. Wagner (cited in Henle's Handbuch der Systematischen Anatomie des Menschen, Bd. I. 3te. Abtheilung, p. 24) who found an accessory fasciculus of the Trapezius inserted into the Mastoid process, and remaining separate as far as the Acromion. The numerous dissectors, who will be busy in our medical schools during the ensuing winter, might do good service by attending to the variations of the Trapezius; and indeed of all those muscles whose attachments in man differ widely from those presented by the apes—e.g. the Flexor pollicis proprius, the Extensor indicis, and the Interossei of the hand: the Tibialis anticus, Extensores digitorum brevis, commmunis digitorum, hallucis longus, Flexor brevis digitorum, Transversus pedis, and Interossei of the foot. We shall be glad to receive and to record examples of such varieties.—[Eds.]
- ↑ This muscle is clearly represented in Man by the tendinous band which, as Halbertsma has shown (Henle, l.c. p. 183) constantly connects the long head of the Triceps with the Latissimus dorsi.—[Eds.]
- ↑ Proceedings of the Zool. Society, vol. i. p. 19.
- ↑ Encyclopédie Anat. tom. iii. p. 202.
- ↑ Mr. C. J. Hallett, Edinburgh Medical and Surgical Journal, 1847.
- ↑ Anat. Comp. Recueil de Planches de Myologie, dessinées par G. Cuvier.
- ↑ The muscles known as Extensores primi intermodii pollicis, Indicis and Minimi digiti, appear to be mere isolated remnants of the complete second or deep extensor digitorum found under various forms in the lower Mammalia.—[Eds.]
- ↑ Vesalii Opera, vol. i. p. 258.
- ↑ Encyc. Anat. tom. iii. p. 230.
- ↑ Wagner, Elements of Comp. Anatomy, translated by Tulk, p. 19.
- ↑ And sometimes this muscle is double and its deeper division gives three tendons, to the 2nd, 3rd and 4th fingers. See Henle, l.c., p. 213.
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