Based on 882 skeletal specimens comprising 444 males and 438 females, the vertebrae of Japanese macaques, Macaca fuscata fuscata, were examined. Numerical variation was determined by counting ribs and by counting facets. No sexual difference was significant in overall distribution of frequencies. The number of cervical vertebrae was invariably seven. The ranges of variation in thoracic, lumbar, sacral, and caudal vertebrae were 12-13, 6-8, 2-4, and 7-11, respectively. The maximum number of caudals exceeds 12, though unconfirmed. The ranges of variation in thoracolumbar, lumbosacral, and thoracolumbosacral vertebrae were 18-20, 9-11, and 21-24, respectively. These variations cannot be fully explained by thoracization, lumbarization, and/or sacralization. The range of variation in vertebrae with thoracic type of prezygapophyseal facets was 8-11, which is wider than that reported previously. Vertebrae are repetitive units with numerical variation. It is impossible to homologize each vertebra among individuals. A new paradigm is needed in order to understand the numerical variation of the vertebral column.
In an attempt to investigate the relationships between ontogenetic, static adult and interspecific allometry, long limb bones of closely related macaques (Macaca mulatta, Macaca fascicularis, Macaca fuscata fuscata and Macaca fuscata yakui) were studied. Sex differences of intralimb allometry were also investigated. Principal component analyses were applied to the maximum length of bones to provide multivariate assessments of relationships between ontogenetic and static adult allometries. Static adult and ontogenetic allometries were different in M. fuscata and M. mulatta, but coincided in M. fascicularis. In interspecific comparison of ontogenetic and static adult allometries, M. fascicularis showed a unique allometric tendency. Analyses of bivariate allometries revealed that sexual dimorphism was a result of ontogenetic scaling (time hypermorphosis). The difference between subspecies of Japanese macaques (M. fuscata fuscata and M. fuscata yakui) was also explained by ontogenetic scaling. A vertical transposition was observed in the ontogenetic patterns of interlimb allometries among the three species. This relationship produced an interspecific positive allometry of the hindlimb compared with the forelimb, which differed from the general trend among nonhuman primates.
Postcranial skeletons were observed and measured on 87 adult Japanese macaques of known chronological age. Forty-three individuals were sacrificed after laboratory experiment. Significant linear regressions against age were observed on diameters and measurements of cross-sectional geometry at mid-length of the humerus and the femur. The older bones showed geometrically greater robusticity against the bending and torsional moments. The materials from the experimentally sacrificed animals showed the same tendency. Geometrical robusticity will compensate the weakening of the bone substance with aging. Articular surfaces and epiphyses also became large with aging. The large ends will again compensate the weakening of the substance in these parts of bone. Females had smaller and more gracile bones than males through the age ranges of adulthood. Many epiphyseal unions belonging to the trunk unite after the maturation of appendicular limb bone length. A great deal of variation was noted in the union completion of adult individuals.
In order to know the relationship between postnatal growth and sexual dimorphism in the cranium of the Japanese macaque, 139 sex-known skulls of the species, which were graded into the nine “dental ages” by means of the dental eruption sequence, were measured on 17 craniometric items. The number of the measurements showing significant sex differences, all of which favored males, increased from two in infant sample (dental age 2) to 14 in adult sample (dental age 9). However, the increase was not monotonic. In dental ages 4 and 5, no linear dimension showed significant sex differences. Furthermore, the females exceeded the males in 47.1% of the cranial dimensions at dental age 4 ranging approximately 2.75 to 3.5 years, which was considered to be the period of the female adolescent growth spurt in the cranial dimensions.
The postnatal growth of Japanese monkeys (Macaca fuscata) was analyzed cross-sectionally by the Spline Function method. Growth patterns were expressed by both distance and velocity curves. The entire growth period of the Japanese monkey is composed of four stages: from birth to two years of age when the growth velocity decreases rapidly; from two to three and a half (in females) or four and a half (in males) years of age when the velocity stays constant or growth accelerates; from those ages to eight years of age when the velocity decreases again to zero; and after eight years of age when growth no longer occurs. The sex difference between ages at full maturation is not large. Variations in growth patterns were compared among four groups of Japanese monkeys: the Koshima, Shiga and Yakushima groups and a Standard group. Characteristics of growth patterns were also compared among several species of Cercopithecids.
The palmar dermatoglyphics of 461 Japanese macaques (Macaca fuscata) were studied. The sample was divided into five groups according to geographical location, and included four groups of the subspecies Macaca f. fuscata and one group of the subspecies M. f. yakui. Chi-square analysis of group differences in the frequencies of dermatoglyphic pattern type and ridge direction showed significant intraspecific differentiation. The two groups showing the most differences from the other three groups were the subspecies Macaca f. yakui (YAKUS group) and the northernmost group of M. f. fuscata (SIMOK group) from the Shimokita Peninsura. Cluster analysis applied to pattern intensity values, which were derived from the pattern types, confirmed the greater biological distance of the SIMOK and especially the YAKUS groups from the others. The extent of intraspecific variation observed in the dermatoglyphic system may reflect the operation of genetic drift in these insular populations.
Anatomy of the intrinsic hand muscles in the Japanese monkeys was studied with an improved method to dissect the muscles and nerves in water after removal of the skeletal framework. The thenar eminence contained four muscles, namely m. abductor pollicis brevis, m. opponens pollicis, m. flexor pollicis brevis, and m. adductor pollicis. The hypothenar eminence contained four muscles, namely m. palmaris brevis, m. abductor digiti minimi, m. flexor digiti minimi brevis, and m. opponens digiti minimi. Majority of the thenar muscles are fused more or less with each other, so that clear separation of these muscles was difficult. The lumbrical muscles arose from the palmar parts of four main tendons of the deep flexor muscle to the second, third, fourth, and fifth digits. The mm. contrahentes arose mainly from a medial tendinous septum attached on the palmar surface to the third metacarpus, and included three muscles destined to the second, fourth and fifth digits. The interossei were found on the radial side of the second, third, fourth and fifth finger as well as on the ulnar side of the second, third and fourth finger. The intrinsic hand muscles in the Japanese monkey received innervation either from the median or the ulnar nerve. Branching pattern of these nerves to the individual muscles was fundamentally similar to those in man except for the fact that the median and the ulnar nerve in the Japanese monkey do not communicate to make a loop in the thenar muscles. A separate branch from the median nerve to the deep head of m. flexor pollicis brevis (accessory recurrent nerve) was described for the first time in the macaque monkey.
Spatial fibre architecture of the deltoid muscles in five Japanese macaques was observed and functionally analysed to compare it with that of the adjoining pectoral muscles. The fibre bundles of the deltoids possess a twisted and radiating architecture, as do those in the pectorals, and are basically arranged symmetrically about the central fibre of the acromiodeltoid. Unlike those of the pectorals, the bundles of deltoids do not exhibit any crossing structure. These structural features of the deltoids are thought to have been formed through evolutionary modifications in the mammal-like reptiles and primitive mammals, which have disposed the humerus more perpendicularly while simultaneously preserving the deltoids as a single-joint muscle. The lateral shift in the cleidodeltoid and the accompanying clavicular origin of the pectoralis in brachiators and human are suggested to have been formed concomitantly with the flattening of the thorax as one of the evolutionary traits in primates.
Hand positions of Japanese macaques were observed during stable ground standing. It was revealed that Japanese macaques preferentially utilize the digitigrade hand position. This agrees with previous claims that terrestrial primates tend to be digitigrade (e.g., Napier and Napier, 1967). In the digitigrade hand position, the second to fifth metacarpophalangeal joints are hyperextended with the metacarpi kept vertical. The proximal articular surface of the basal phalange is excavated proximodorsally in Japanese macaques to allow the hyperextension of the metacarpophalangeal joint. This skeletal specialization was observed in the digitigrade baboon and the palmigrade colobus monkey also. However, it was not seen in New World monkeys, apes and human. This skeletal feature may suggest a retention of the semi-terrestrial origin of cercopithecids.
Individual variation in composition of myofiber types (SO, FOG, and FG) was examined in the m. triceps surae and m. flexor digitorum superficialis of male and female Japanese macaques. The m. soleus generally had more SO myofibers than FOG and FG myofibers. The m. gastrocnemius and m. flexor digitorum superficialis had more FG myofibers than the other myofiber types. No sex-related differences in composition of myofiber types were noted in the muscles. Great differences in myofiber type percentages existed among the animals. The proportion of SO myofibers ranged from 32.8 to 95.9% in the m. soleus, from 8.1 to 50.5% in the m. gastrocnemius caput mediale, from 6.5 to 43.8% in the caput laterale, and from 3.2 to 44.7% in the m. flexor digitorum superficialis. Interindividual differences in myofiber type composition may be determined partially by genetic factors and be due partially to differences in capacity for changing myofiber types to meet postural or locomotory requirements.
The microvascular architecture of the optic region of the retina in the Japanese monkey was revealed under SEM utilizing microcorrosion casts by Ohta's method (1990). At the optic nerve disc, the central retinal artery radiated to four primary retinal arterioles. A dense retinal capillary network between these vessels extended outwards and showed regional differences in density. At the optic nerve disc part, the network developed into a multi-laminar structure containing the radial peripapillary capillaries at the innermost layer. At the macula, the retinal capillaries formed a ring around the central fovea (an avascular area). At the equatorial part, the network was observed to be double-layered: a superficial capillary network (on the vitreous side) located in the nerve fiber layer with a capillary-free zone (CFZ) 30-50μm in width around arterioles and a deep capillary network (on the choroid side) located at the external nuclear lamina without the CFZ. At the serrata ora, the network diminished to a single layer with coarse ovoid meshes, and the CFZ developed to 50-70μm in width around arterioles. In conclusion, the microvasculature of the retina in the Japanese monkey showed regional variations in proportion to the fine structures of the retinal layers. CFZ occurred since the retinal capillaries were located in the same level as the arterioles.
Origins and pathways of the hepatic artery were investigated in 9 Japanese and 4 rhesus macaques. In one case of Japanese macaques, the liver received a double arterial supply from an accessory and ordinary hepatic arteries. The accessory hepatic artery arose from the celiac artery and supplied two right lobes and the gallbladder. In five cases of Japanese macaques and in all cases of rhesus macaques, the common hepatic artery passed behind the pylorus and the pancreas. This course corresponds to one of the two pathways of the accessory hepatic artery of the humans and chimpanzees. In remaining four cases of Japanese macaques, the course of the common hepatic artery corresponds to the pathway of the ordinary hepatic artery of the humans and chimpanzees. The celiac artery of the macaques tends to arise at a more caudal level of the aorta than in the humans and chimpanzees.
There has been no anatomical study on the lymphatic system of Japanese monkey. In the present study, four Japanese monkeys (Macaca fuscata fuscata, 2 males and 2 females) were studied on the lymphatic system injected with the Indian-ink. The jugular, subclavian, bronchomediastinal and lumbar lymphatic trunks were well demonstrated, but the intestinal trunk was not fully revealed in this study. In this study the lymphatic system of Japanese monkeys was compared with those of tree shrews, lemurs, marmosets and rhesus monkeys using the idea of Lymphocentrum (Lc), which was introduced by Baum (1930) and Grau (1943). It has been known that there are 15 Lc in tree shrews, 15 Lc in lemurs, 16 Lc in marmosets, and 16 or 18 Lc in rhesus monkeys. The present study showed 15 Lc including 27 lymph nodes in Japanese monkeys. It seems that the Japanese monkey is rather more primitive than the rhesus monkey in the development of lymphatic system.
The present study demonstrated the three-dimensional organization of the collagen and elastin fibers of the lung in the Japanese monkeys, Macaca fuscata as revealed by alkali-maceration/scanning electron microscope technique. The collagen fibers, which were bundles of collagen fibrils, were repeatedly divided and fused to form a network along the alveolar duct. The collagen fibers in the alveolar duct branched and entered the alveolar septa, where the fibers again repeated branching and fusing and formed thin networks. Thick collagen fibers around the alveolar mouths took significant degree of zig-zag or spiral courses. The elastin fibers were condensed around the alveolar mouths, but there were also elastin fibers between the adjacent alveolar mouths. Within the alveolar septa were course network of elastin fibers.
Segi's cap, an aggregation of the basal-granulated cells in the intestinal villi of the fetal Japanese monkey was investigated by means of light microscopy and immunocytochemical techniques. Characteristic Segi's caps were observed at the tips of the villi in the duodenum and upper jejunum in fetal Japanese monkeys, aged 120 and 140 days. The Segi's cap of Japanese monkeys is characterized by the following morphological features: 1) There are relatively fewer caps per section in comparison with humans. 2) The number of basal-granulated cells of the cap is also less than in humans. 3) The characteristic indentation at the center of the Segi's cap, reported in humans, cattle and pigs is only rarely present. 4) Argentaffin cells, which are now known as serotonin-containing cells, are present in the monkey Segi's cap. 5) Somatostatin-, motilin-and CCK-immunoreactive cells are found in the monkey Segi's cap.
Histological characteristics of male reproductive organs were observed macrographically and microscopically in Japanese macaques aged 20 years old or more. As the senility proceeded, testicular weight and the diameter of the seminiferous tubules decreased. Likewise, the weights and epithelial heights of the seminal vesicle and prostate gland decreased in old males. Histologically, a proliferation of interstitial tissue was notable in every organ examined. Seminiferous epithelium decreased in height as the age of animal approached thirty years. Similarly, disorder of cellular association and decrease in the number of spermatogenic cells were observed in the seminiferous tubules.