Bengal Slow Loris - Anatomy and Physiology

Anatomy and Physiology

The Bengal slow loris is the largest species of slow loris, weighing 1 to 2.1 kg (2.2 to 4.6 lb), and measuring between 26 and 38 cm (10 and 15 in) from head to tail. It has a skull length of more than 62 mm (2.4 in). It has dense, woolly, brown-gray fur on its back and white fur on its underside. It also has a clear dark stripe that runs up to the top of its head, but does not extend laterally towards the ears. Its forearm and hand are almost white. The limbs of the pelvis vary in color from brown to nearly white, and the feet are always pale. Moulting may cause seasonal variations in the color of the dorsal surface. Like other slow lorises, its tail is vestigial and it has a round head and short ears. It has a rhinarium (the moist, naked surface around the nostrils of the nose) and a broad, flat face with large eyes. Its eyes reflect a bright orange eye shine. On its front feet, the second digit is smaller than the rest; the big toe on its hind foot opposes the other toes, which enhances its gripping power. Its second toe on the hind foot has a curved "toilet-claw" that the animal uses for scratching and grooming, while the other nails are straight.

In addition to being smaller than the Bengal slow loris, the sympatric Sunda slow loris also differs in its coloring: it does not have the pale areas of the head, nape and shoulders, and its overall color is a tawny- or golden-brown. The pygmy slow loris (N. pygmaeus) is much smaller, with a skull length less than 55 mm (2.2 in). It also lacks the dark dorsal stripe of the Bengal slow loris, has dark brown fur, and longer ears.

The Bengal slow loris has a small swelling on the ventral side of its elbow called the brachial gland, which secretes a pungent, clear oily toxin that the animal uses defensively by wiping it on its toothcomb. The oil has been analyzed using gas chromatography coupled to mass spectrometry, and it has been shown that almost half of the several dozen volatile or semi-volatile chemicals present do not occur in the closely related pygmy slow loris. The most predominant component was the phenolic compound m-cresol. The authors of the study suggest that the chemically complex oils may help the lorises communicate with each other, allowing them to transmit by scent information about sex, age, health and nutritional status, and dominance.