American Journal of Anatomy

doi: 10.1002/aja.1001250301pmid: N/A

Kruger, Lawrence; Maxwell, David S.

doi: 10.1002/aja.1001250302pmid: 5790993

Numerous optic nerve fibers persist for a period of up to 20 months following enucleation in reptiles, although it is unlikely that a significant number of efferent fibers are present. After varying survival periods, almost all nerve fibers display distinct morphological changes probably associated with degeneration, but most features previously associated with early stages of degeneration can be seen in long‐survival material except for the early and rapid loss of all non‐myelinated fibers and a honeycomb tubular degeneration associated with the inner and outer myelin layers. Distinct sequential stages of axon and myelin degeneration could not be ascertained despite the slow rate of degeneration in poikilotherms. The varieties of abnormal axon morphology are documented and considered in terms of current light microscopic staining methods.

Bernard, George W.; Pease, Daniel C.

doi: 10.1002/aja.1001250303pmid: 5790994

Calvariae of fetal mice were investigated with electron microscopy in order to demonstrate initial stages of immature, membrane bone calcification. As a consequence, nucleation sites for initial calcification of hydroxyapatite crystals in woven bone were found in extrusions from osteoblasts within the osteoid. Growth of the crystals epitaxially from these initial calcification loci into the surrounding collagen was spherulitic, forming discrete spheres referred to as “bone nodules”. These nodules, when coalesced, formed seams of bone. Decalcified, the organic substructure of the bone nodules was revealed. It contained a centrally disposed initial calcification locus, a peripheral zone of decomplexing collagen and an intermediate zone of altered collagen. Fully formed collagen fibrils remained interposed between most of the coalesced nodules. Polysaccharides were localized within the initial calcification locus and in the peripheral zone of the bone nodules where collagen was shown to be decomplexing.

Cornell, Richard; Padykula, Helen A.

doi: 10.1002/aja.1001250304pmid: 5790995

The distal small intestine of the albino rat has the capacity to absorb protein and particulate matter during the suckling period. Ultrastructural and cytochemical aspects of this absorptive phenomenon were examined in the ileum. Soon after the initial ingestion of milk, a large, yellow, smooth membrane‐limited, protein body appears in the immediate supranuclear region of ileal absorptive cells and, also, many small vacuoles and membrane‐limited droplets arise between this body and the microvilli. Exogenous protein enters an elaborate superficial tubular system and is segregated in membrane‐limited vacuoles and droplets and, then, appears in the supranuclear body. The body and adjacent membrane‐limited droplets are basophilic, periodic acid‐Schiff positive, and rich in hydrolytic enzymes (acid phosphatase, ATPase, thiamine pyrophosphatase, alkaline phosphatase, esterase). The results suggest the presence of a highly developed lysosomal system during the period of protein absorption. Additional cytological features of the absorptive cells are presented.

Humphrey, Tryphena

doi: 10.1002/aja.1001250305pmid: 5790996

The status of the palatal shelves of shelves of human fetuses (before, during and after palatal shelf elevation) was correlated with mouth opening reflexes recorded cinematographically by Doctor Davenport Hooker for many of the same fetuses. Some deductions and conclusions follow.

Pearson, Anthony A.; Sauter, Ronald W.

doi: 10.1002/aja.1001250306pmid: 5790997

In human embryos and fetuses, a small bundle of nerve fibers from the anterior and posterior vagal trunks descends between the layers of the hepatogastric ligament. These fibers pass to the region of the junction of the umbilical vein with the ductus venosus. At this junction, there is a slight thickening of the muscular wall. Nerve fibers pass to this junction and the proximal portion of the umbilical vein.

Sekhon, Sant S.; Beams, H. W.

doi: 10.1002/aja.1001250307pmid: 5790998

The cytological changes accompanying the development of red blood cells of trout were studied. These changes appear to parallel closely those seen in the maturation of red blood cells of mammals. Immature erythrocytes of the trout contain mitochondria, Golgi complex, rough and smooth endoplasmic reticulum, centrioles, bundles of microtubules and numerous ribosomes in their cytoplasm. With progressive differentiation and maturation such cells appear to shrink in size, acquire a biconvex ellipsoid form, lose most of their cytoplasmic organelles and concomitantly increase their hemoglobin content. Mitochondrial degradation begins early in the process of maturation and usually consists of the following sequence of morphological changes within them: the appearance of small dense bodies, degeneration of the cristae and the formation of lamellar bodies. Degenerating mitochondria are often observed bulging from the surface of the cell, suggesting that they are in the process of being extruded from it. However, this observation does not preclude the possibility that mitochondria may also be disposed of in situ through the action of lysosomal enzymes. It is suggested that the disappearance of mitochondria and other cytoplasmic organelles contributes to the volumetric shrinkage which accompanies the maturation of trout red blood cells. The existence of an equatorially oriented “marginal band” of microtubules has been confirmed in this material in agreement with studies on other species. A band of microtubules was also observed in trout thrombocytes. It is concluded that the marginal band plays an important role in the maintenance of the flat ellipsoidal shape of these cells as has been suggested by other investigators studying other vertebrate forms.