The mature vertebrate retina is a highly complicated array of several kinds of cells, capable of receiving light impulses, transforming them into neuronal membrane currents, and transmitting these in a meaningful way to central processing. Before it starts to develop, it is a small sheet of unconspicuous cells, which do not differ from other cells of the central nervous system. The chain of events which lead to the trans- formation from this stage into that of highly specialized cells ready to fulfll a specific task, is usually called "differentiation. " Originally, this word indicated...

The study of the development of the spinal cord has a relatively long history. The spinal cord was singled out as a favorable site when cytological techniques were first applied to the study of the embryonic development of the nervous system. Bidder and Kupffer (1857), using the new procedure of hardening nerve tissue with chromic acid (Hannover 1844), made an investigation of spinal cord development in fetal sheep. They reported that the cellular central mass of the spinal cord develops before its fibrous envelope, deducing from this that the fibers of the white matter of the embryonic...

1. 1 Brief History The diversity of cells constituting the central nervous system did not deceive last century neurohistologists in recognizing that this organ contained essentially two cell types: the nerve cells, or as termed according to the emerging concept of neural contiguity, the neurons, and the neuroglial cells. Neurons were clearly shown to be the means of excitability, impulse generation, impulse transmission, and connectivity in the neural tissue. The neuroglia, as indicated by its name (YAloc=cement or glue) given by Virchow (1860), was thought to be the cement- ing material...

During development two strongly interrelated processes can be discerned in the central nervous system (eNS), namely morphogenesis and histogenesis. Most neuroembryological studies deal with histogenetic features virtually with- out any morphological elucidation. It must be stressed, however, that histogen- etic investigations should be based upon a thorough knowledge of morphogene- sis. This holds especially for the forebrain, which during development is sub- jected to drastic transformations, particularly when only two-dimensional sec- tions are used. Therefore the present study on...

At the end of the nineteenth century, controversy arose as to precisely when the first glial cells originate during development of the central nervous system, and to date, the issue has not been satisfactorily resolved. His (1889, 1890) noted that, even in the earliest developmental stages of the germinallayer, there appeared to be two distinct cell types. The cells which he called Spongioblasten were thought to be glial precursors from which all mature glial cells derive; Keimzellen, in contrast, were regarded as forming 1 neurons. His was working on the assumption that the very first...

In the search for explanations for differences in the shape of skulls and their phylogenetic development, the morphology of the skull must be seen in connec- tion with the functions it has to perform. The skull encloses the brain and the sense organs and provides them with physical protection. It also houses the initial parts of the respiratory and digestive systems and together with the jaws constitutes a tool capable of cutting and grinding food. The skull must be able to withstand forces imposed upon it by chewing, by movement of the head, by the weight of the head itself, and by impact...

Insectivores are considered to be primitive among the Eutheria and are therefore of particular interest (Romer 1966). In spite of this basal position of the group there are only few papers dealing with the structure of the female reproductive tract in insectivores. Erinaceus has been studied by Deanesly (1934), Talpa by Matthews (1935), some Centetinae from Madagascar by Feremutsch (1948) and Feremutsch and Strauss (1949), and Tenrec by Nicoll and Racey (1985). Among the Soricidae (shrews), Sorex (Brambe1l1935), Blarina (Pearson 1944), Neomys (price 1953), Suncus (Dryden 1969), and Crocidura...

Though more than 300 years have elapsed since the first description of the peculiar course of the spinal accessory (XI) nerve by Willis (1664), the crucial problems concerning what is known as accessory field of musculature and its innervation are still unsolved and a matter of controversy. Like the bulbar XI, the spinal XI nerve is commonly regarded as originally a branch of the vagus and, therefore, as a cranial nerve (Fiirbringer 1897; Gegenbaur 1898; Lubosch 1899). However, whether this nerve is of special visceral or somatic derivation is still debated. The conventional distinction...

According to Valentin (1833) and Luschka (1862), the first description of the structure now known as the carotid body must be ascribed to a Swiss physiolo- gist - Albrecht von Haller - who, in 1762, called it the ganglion exiguum. This claim, however, may be erroneous, for Tauber (1743) described a struc- ture at the bifurcation on the common carotid artery and called it the ganglion minutum. Andersch (1797) reprinted the text of a study made by his father between 1751 and 1755. The original printing of this work had apparently been sold as waste paper Andersch called the organ the ganglion...

Many mammalian species living at medium or higher latitudes show marked annual cycles in various morphological and functional properties. There is a clear cycle of the reproductive activity ranging from a fertile to an infertile state in both the male and female. Such an annual periodicity can be regarded as an adaptation to seasonal changes of environmental conditions such as cli- mate and nutrition, ensuring that birth and development of the litter are re- stricted to a favorable season. These annual cycles consist of cyclic changes of exocrine and endocrine gonadal function, in the...