Comparative anatomical study of the forearm extensor muscles of Cebus libidinosus (Rylands et al., 2000; Primates, Cebidae), modern humans, and other primates, with comments on primate evolution, phylogeny, and manipulatory behavior.

Despite its abundance in Latin America, and its remarkable ability to use tools, there are only a few myological studies on the capuchin monkey, Cebus libidinosus. In the present study, we dissected the forearm extensor muscles of six adult males and two adult females of this species. We describe these muscles and compare them with those of other primates dissected by us and by other authors. The forearm extensor muscles of Cebus monkeys are, in general, more similar to those of other platyrrhines than to distantly related taxa that use tools, such as chimpanzees and modern humans, with three main exceptions: contrary to most other platyrrhines, (1) in Cebus, chimpanzees and modern humans the extensor pollicis longus usually inserts onto Digit I, and not onto Digits I and II; (2) in Cebus the abductor pollicis longus has two separate tendons, as is the case in chimpanzees, and in modern humans (where one of these tendons is associated with a distinct belly, forming the muscle extensor pollicis brevis); (3) in Cebus, and in modern humans and chimpanzees, the extensor pollicis longus is not deeply blended with the extensor indicis. Therefore, the Cebus monkeys provide an illustrative example of how phylogenetic constrains and ecological adaptations have been combined to develop a specific myological configuration that, associated with their sophisticated neurological organization, allow them to easily navigate in their arboreal habitats and, at the same time, to finely manipulate objects in order to search for food and to prepare this food for ingestion.

Effects of glycerol and sorbitol on the thermal dependence of the lysis of human erythrocytes by ethanol.

In this work, the effects of 1 mol/L glycerol or sorbitol on the thermal dependence (27-47 degrees C) of the lysis of human erythrocytes by ethanol in saline solution (0.154 mol/L NaCl) have been evaluated. Lysis was monitored by measurement of the absorbance at 540 nm. Ethanol produced either lysis or protection against lysis depending on the conditions. These antagonistic effects are attributed to the existence of expanded (R) and compacted (T) erythrocytes, present under conditions of low and high osmolarity, respectively. The transitions of lysis of the R state and formation and lysis of the T state were all found to be sigmoidally defined. The ethanol concentration at the midpoint of the lysis transition of the R state (D(50R)) was found to decrease with increasing temperature and osmolarity. In the presence of glycerol or sorbitol, an increase in temperature led to smaller decreases in D(50R) and osmotic protection against lysis. The ethanol concentration at the midpoint of formation (S(50T)) and lysis (D(50T)) of the T state also decreased with increasing temperature and osmolarity. Lysis of R state erythrocytes is determined by the chaotropic action of ethanol, but the formation and lysis of T state erythrocytes are determined by osmotic pressure effects.