Doctor of Philosophy
Anatomy & Neurobiology
Duane E. Haines
The function of the central nervous system cannot be understood from inspection of a single region, for each cell and fiber has discrete connections. Therefore, a study of the nervous system requires distinct approaches. One fundamental approach has been the study of comparative neuroanatomy.
In a comparative study of the evolution of the primates and subsequently man, the investigator is confronted with a variety of animal forms. Each form represents an end product of a long vertical line of evolutionary development. The problem is to try to reconstruct the vertical line (ancestral forms) from the horizontal end products (extant forms).
The order Primates has two suborders: (1) the Prosimii - composed of six families - Tupaiidae, Lemuridae, Indriidae, Daubentoniidae, Lorisidae, and Tarsiidae and (2) the Anthropoidea - also composed of six families including the Old and New World monkeys, the great apes and man. One group of the suborder Prosimii is the family Lorisidae. The living members of the family are represented by the lorises of India and Southeast Asia and the galagoes and pottos of Africa. Characters these animals share with the higher anthropoid primates are seen in the osteology of the middle ear and the medial wall of the orbit (Le Gros Clark, 1959). They also have orbits encircled by bone, three kinds of teeth, a well developed caecum, true nails and a pseudo-opposable thumb. In habit, these animals are omnivorous, nocturnal and arboreal. In progression, the lorisoids are less tied to the quadrupedalism of many lemurs (Osman Hill, 1953). The lorises have a slow deliberate mode of hand-over-hand locomotion, their limbs are subequal in length. In contrast, the galagos locomote by a rapid, saltatory behavior and have pelvic limbs much longer than pectoral limbs. Both of these means of progression effect an orthograde (erect or semi-erect) posture of the trunk and a tendency for a different mode of balancing the head on the spine.
Some authors regard the vertical clinging and leaping of galagos as the earliest locomotor specialization of primates (Napier and Walker, 1967; Napier, 1967). From the post-cranial osteology of early Miocene Lorisidae (Walker, 1970) and from a comparative osteological, behavioral and paleontological study (Napier and Walker, 1967), it appears that this locomotor pattern was present in early Eocene and subsequent Miocene prosimians. These authors conclude that vertical clinging and leaping is the earliest known primate locomotor specialization and preadaptive to some or possibly all subsequent patterns of primate progression—quadrupedalism, brachiation and bipedalism.
Although comparative neuroanatomical investigations have utilized the anthropoid primates, (mainly Macaca) rodents and carnivores (chiefly the cat), the prosimian primates have been relatively ignored. Yet their locomotor behavior and their propensity toward bipedalism make them an interesting model for a study of central nervous pathways related to locomotion.
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