WThe gluteal sulcus is an area of the body of humans and anthropoid apes, described by a horizontal crease formed by the inferior aspect of the buttocks and the posterior upper thigh. The gluteal sulcus is formed by the posterior horizontal skin crease of the hip joint and overlying fat, and is not formed by the lower border of the gluteus maximus muscle, which crosses the fold obliquely. It is one of the major defining features of the buttocks. Children with developmental dysplasia of the hips are born with uneven gluteal folds and can be diagnosed with physical examination and sonogram.
WA grooming claw is the specialized claw or nail on the foot of certain primates, used for personal grooming. All prosimians have a grooming claw, but the digit that is specialized in this manner varies. Tarsiers have a grooming claw on second and third toes. With one possible exception, in the suborder Strepsirrhini, which includes lemurs, galagos and lorises, the grooming claw is on the second toe. The possible exception is the aye-aye, which has claws instead of nails on toes 2 through 5. There is some debate concerning whether any of these claws are grooming claws. Less commonly known, a grooming claw is also found on the second pedal digit of night monkeys (Aotus), titis (Callicebus), and possibly other New World monkeys.
WThe philtrum, or medial cleft, is a vertical indentation in the middle area of the upper lip, common to many mammals, extending in humans from the nasal septum to the tubercle of the upper lip. Together with a glandular rhinarium and slit-like nostrils, it is believed to constitute the primitive condition for at least therian mammals. Monotremes lack a philtrum, though this could be due to the specialised, beak-like jaws in living species.
WThe basal ganglia form a major brain system in all species of vertebrates, but in primates there are special features that justify a separate consideration. As in other vertebrates, the primate basal ganglia can be divided into striatal, pallidal, nigral, and subthalamic components. In primates, however, there are two pallidal subdivisions called the external globus pallidus (GPe) and internal globus pallidus (GPi). Also in primates, the dorsal striatum is divided by a large tract called the internal capsule into two masses named the caudate nucleus and the putamen—in most other species no such division exists, and only the striatum as a whole is recognized. Beyond this, there is a complex circuitry of connections between the striatum and cortex that is specific to primates. This complexity reflects the difference in functioning of different cortical areas in the primate brain.
WSexual dimorphism describes the morphological, physiological, and behavioral differences between males and females of the same species. Most primates are sexually dimorphic for different biological characteristics, such as body size, canine tooth size, craniofacial structure, skeletal dimensions, pelage color and markings, and vocalization. However, such sex differences are primarily limited to the anthropoid primates; most of the strepsirrhine primates and tarsiers are monomorphic.
WThe sublingua ("under-tongue") is a muscular secondary tongue found below the primary tongue in tarsiers and living strepsirrhine primates, which includes lemurs and lorisoids. Although it is most fully developed in these primates, similar structures can be found in some other mammals, such as marsupials, treeshrews, and colugos. This "second tongue" lacks taste buds, and in lemuriforms, it is thought to be used to remove hair and other debris from the toothcomb, a specialized dental structure used to comb the fur during oral grooming.
WThe brow ridge, or supraorbital ridge known as superciliary arch in medicine, refers to a bony ridge located above the eye sockets of all primates. In Homo sapiens sapiens the eyebrows are located on their lower margin.
WA toothcomb is a dental structure found in some mammals, comprising a group of front teeth arranged in a manner that facilitates grooming, similar to a hair comb. The toothcomb occurs in lemuriform primates, treeshrews, colugos, hyraxes, and some African antelopes. The structures evolved independently in different types of mammals through convergent evolution and vary both in dental composition and structure. In most mammals the comb is formed by a group of teeth with fine spaces between them. The toothcombs in most mammals include incisors only, while in lemuriform primates they include incisors and canine teeth that tilt forward at the front of the lower jaw, followed by a canine-shaped first premolar. The toothcombs of colugos and hyraxes take a different form with the individual incisors being serrated, providing multiple tines per tooth.