Development of the Lacrimal Apparatus in the Rabbit (Oryctolagus cuniculus) and Its Potential Role as an Animal Model for Humans.

Rabbits have been proposed as a model organism for the human lacrimal apparatus (LA), including the nasolacrimal duct (NLD), based principally on comparative studies of adult morphology; however, little is known about its development. The NLD first appears as an incomplete primordium in the subcutaneous region of the primordial eyelid and subsequently elongates to reach the naris. One posterior and three anterior orbital glands are present fetally although one of the anterior glands is soon lost. The NLD follows a tortuous path and passes through a bony canal consisting of lacrimal, maxilla, and maxilloturbinal bones at different regions. Although early developmental similarities exist to haplorhine primates, the narial opening of the NLD resembles strepsirrhines. This distinction, along with the ductal and glandular differences at the orbital end of the NLD, indicates that rabbits may be a poor model for LA drainage in primates, specifically humans.

Is it or isn't it? A reexamination of the anterior orbital glands of the fat-tailed Dunnart Sminthopsis Crassicaudata (Dasyuridae: Marsupiala) and a reevaluation of definitions for the Harderian gland.

The anterior orbital glands of tetrapods, which include the Harderian and nictitans glands, can usually be differentiated either anatomically (nictitans gland is more anterior) or histochemically (Harderian gland secretes lipids). However, conflicting statements exist in the literature about the presence and identity of these glands. Two previous studies on Sminthopsis crassicaudata (Dasyuridae: Marsupiala) either failed to note any anterior ocular glands or used no histochemical analyses. This study reexamined the structure of the anterior orbital glands of S. crassicaudata. Histological, histochemical, and ultrastructural examination revealed three glandular units: two of which are located superficially in the nictitating membrane, the third lying deeper in the connective tissue. The ducts of these three glandular units all open onto the corneal aspect of the nictitating membrane. These cells contain mainly serous granules with sparse intracellular lipid droplets. The nomenclature of these structures depends upon the definition used. According to the anatomical definition, S. crassicaudata has two glands: anteriorly the nictitans and posteriorly the Harderian gland. In contrast, if the histochemical definition is used, there is only one gland, but its precise identity cannot be confirmed until the role of the lipid droplets is established. Moreover, the histochemical definition poses additional problems with respect to the mechanism of secretion, multiple secretions, and glandular plasticity. Finally, the unitary definition identifies one deeply subdivided gland with an anterior and a posterior lobe in S. crassicaudata. This last definition is broad enough to accommodate a wide level of anatomical variation in the anterior ocular glands of tetrapods.

One gland, two lobes: organogenesis of the "Harderian" and "nictitans" glands of the Chinese muntjac (Muntiacus reevesi) and fallow deer (Dama dama).

The nictitans and Harderian glands are enigmatic glands situated in the anterior aspect of the orbit. Traditionally, the nictitans and Harderian glands of mammals have been considered to be two fundamentally distinct glands. However, a consistent, unambiguous distinction between these two glands has remained elusive due to conflicting anatomical and histochemical definitions. The Harderian gland was originally described, and first distinguished from the nictitans gland, in adult deer. We examined the organogenesis and histochemistry of the anterior orbital glandular mass in two species of deer (Muntiacus reevesi and Dama dama) to determine whether it comprises two distinct glands or one bilobed gland. The anterior orbital regions of 30 fetal specimens of both species, along with some adult material, were examined histologically. Four stages of glandular organogenesis were observed. Most notably, both glandular portions developed from the same inception point, but the deep lobe developed faster than the superficial lobe. The common inception point and the relationship of the collecting ducts clearly shows that this is a single glandular mass that differentiates into two lobes rather than two distinct glands. Moreover, although the histochemical profiles of the two lobes differ slightly, both lobes produce lipids, which is further indication that these are not profoundly different glands but part of a single, heterogeneously developed gland. Thus, it is proposed that the terms nictitans and Harderian glands, as separate entities, be discontinued and that the entire gland be referred to as the anterior orbital gland (glandula orbitalis anterior), with superficial and deep lobes (pars superficialis and pars profundus, respectively).

Cursoriality in bipedal archosaurs.

Modern birds have markedly foreshortened tails and their body mass is centred anteriorly, near the wings. To provide stability during powered flight, the avian centre of mass is far from the pelvis, which poses potential balance problems for cursorial birds. To compensate, avians adapted to running maintain the femur subhorizontally, with its distal end situated anteriorly, close to the animal's centre of mass; stride generation stems largely from parasagittal rotation of the lower leg about the knee joint. In contrast, bipedal dinosaurs had a centre of mass near the hip joint and rotated the entire hindlimb during stride generation. Here we show that these contrasting styles of cursoriality are tightly linked to longer relative total hindlimb length in cursorial birds than in bipedal dinosaurs. Surprisingly, Caudipteryx, described as a theropod dinosaur, possessed an anterior centre of mass and hindlimb proportions resembling those of cursorial birds. Accordingly, Caudipteryx probably used a running mechanism more similar to that of modern cursorial birds than to that of all other bipedal dinosaurs. These observations provide valuable clues about cursoriality in Caudipteryx, but may also have implications for interpreting the locomotory status of its ancestors.

Septomaxilla of nonmammalian synapsids: soft-tissue correlates and a new functional interpretation. DELETE.

The function of the septomaxilla of nonmammalian synapsids has long been problematic. Distinctive features of this bone, including a prominent intranarial process and a septomaxillary canal and foramen, are characteristic of pelycosaurs and nonmammalian therapsids, but are lost in their mammalian descendants. Numerous contradictory reconstructions have been proposed for the soft anatomy associated with the septomaxilla of nonmammalian synapsids. This review supports the following conclusions: 1) No particular correlation exists between the septomaxilla and the vomeronasal organ (VNO), and the most likely location for the VNO is on the dorsal surface of the palatal process of the vomer; 2) The most likely occupant of the septomaxillary canal is the nasolacrimal duct, which opened either anterior or medial to the intranarial process, near the opening of the VNO duct; and 3) The occupant of the septomaxillary foramen remains uncertain. These conclusions suggest that the functional significance of the septomaxilla in the nonmammalian synapsids is tied to that of the nasolacrimal duct. The association of this duct and the VNO in these animals resembles the condition in Recent amphibians and lepidosaurs, in which the nasolacrimal duct supplies orbital fluids to the VNO, apparently to enhance vomeronasal function. The peculiar shape of the synapsid septomaxilla may have served to collect vomeronasal odor molecules. The changes of the septomaxilla in early mammals, and its nearly complete loss in extant mammals, are probably correlated with a dissociation of the nasolacrimal duct and VNO, and functional changes in both structures.

Nonavian feathers in a late Triassic archosaur.

Longisquama insignis was an unusual archosaur from the Late Triassic of central Asia. Along its dorsal axis Longisquama bore a series of paired integumentary appendages that resembled avian feathers in many details, especially in the anatomy of the basal region. The latter is sufficiently similar to the calamus of modern feathers that each probably represents the culmination of virtually identical morphogenetic processes. The exact relationship of Longisquama to birds is uncertain. Nevertheless, we interpret Longisquama's elongate integumentary appendages as nonavian feathers and suggest that they are probably homologous with avian feathers. If so, they antedate the feathers of Archaeopteryx, the first known bird from the Late Jurassic.