Some anatomic features of the posterior wall of the left atrium, the atrial-pulmonary venous junctions, and the myocardial sleeves extending over the pulmonary veins, as observed in 16 human hearts, are described. Different patterns of direction of the myocardial fibers of the atrial wall were found in the different specimens. The atrial wall between the upper pulmonary veins was consistently thicker than that between the lower ones. Similarly, the sphincter-like structures of the atrial-pulmonary venous junctions were generally more conspicuous, and the myocardial venous sleeves better developed in the superior than in the inferior pulmonary veins. The physiological and pathological implications of these findings are discussed.

SUMMARY Four hundred and eighty foramina transversaria in dry cervical vertebrae of 36 spines and in a number of dissections were studied and classified according to size, shape, and direction of their main diameter. A coefficient of roundness was then elaborated. The variations of foramina appear to follow a pattern at various vertebral levels. The possible factors (in addition to the embryological ones) involved in causing these variations-for example, mechanical stress, size, course, and number of the vertebral vessels-were analysed. The importance of the correct interpretation of the variations in the foramina transversaria in radiographic or computerised axial tomography is discussed. The contribution of the present study to the understanding and diagnosis of pathological conditions related to the vertebral artery and its sympathetic plexus is stressed.

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Six hundred and seventy-two atlas vertebrae of 6 population groups were examined for the presence of a posterior and/or lateral bridge. Of these, 174 (25.9%) presented with partial posterior bridge formation and 53 (7.9%) with a complete bridge. Twenty-six (3.8%) showed some form of lateral bridging. Although controversy exists as to the origin of atlas bridging, the findings of the present study show that aging could be a factor predisposing to complete bridge formation. The clinical significance of bridge formation is discussed with reference to their possible effect on normal vertebral artery function, particularly in rotation.

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✓ A study of connections between C-1, C-2, and the spinal accessory nerve is reported. Four variations are described from anatomical and clinical points of view. Often the only pathway for the sensory fibers of C-1 to reach the spinal cord is through the rootlets of the eleventh cranial nerve.

The myocardial fibres of the posterior wall of the atrio-venous junctions were examined in 35 large domestic mammals. In the majority of specimens a common pattern in the course and organization of the fibres could be observed. The most obvious features were the following: (1) a main circular fascicle surrounding the pulmonary trunks; (2) fibres encircling the atriovenous junctions; and (3) myocardial sleeves extending along the veins, occasionally as far as the lung. The superior part of the left atrial wall was consistently thicker than the inferior section. Individual variations of this wall between the various trunks followed one of four patternsvertical, oblique, horizontal or criss-crossed. Differences between mammal and human hearts were found regarding the number of pulmonary trunks, the presence of the oblique vein of the left atrium, and the extension of the myocardial sleeves on the caval vein. This extension on the caval vein continues over the end of the azygos vein in animals. The functional significance of the structures described in this study is discussed.The presence of sleeves of atrial myocardium continuing over the pulmonary veins and venae cavae have been observed in various mammals and human hearts (Favaro, 1910;Brown, 1913;Papez, 1920;Auer, 1948;Los and Dankmeijer, 1956;Neill, 1956; Thomas, 1959;Klavins, 1963;Kosir, 1964;Carrow and Calhoun, 1964;Nathan and Eliakim, 1966). Although these sleeves are commonly neglected in anatomical textbooks and medical literature (Bourdelle, 1920;Bruni and Zimmerl, 1951 ;Sisson, 1953 ;Miller, Christensen, and Evans, 1964;May, 1964), they may perhaps be of functional importance. Previous studies in dogs (Eliakim, Stern, and Nathan, 1961) and humans (Nathan and Eliakim, 1966) disclosed that the atrial wall around the superior veins was thicker and the sphincter-like arrangement of the fibres was generally more distinct around the superior veins. It was also observed that the myocardial sleeves of the superior veins usually extended further towards th2 lung than did the sleeves of the inferior veins.In the present work, hearts of large mammals were studied with the hope that their dissection might contribute more anatomical details about the atrio-pulmonary and atrio-caval vein junctions, in order to permit a better understanding of the functions of these structures. MATERIAL AND METHODSThe hearts of 35 animals-17 sheep, 9 cattle, 5 pigs, 2 donkeys, 1 horse, and 1 camel-of various ages, both male and female, were dissected for the present study. The heart, pulmonary vessels, and part of the lungs were removed together in all cases. The anterior caval vein was cut above the opening of the azygos vein and the posterior caval vein was cut at the level of the diaphragm. The atria were separated from the ventricles at the level of the atrioventricular sulcus, so that they could be examined from both the inner and outer aspects. Using a micrometer caliper with a rachet stop, the thickness of the posterior wall of the left atrium was measured at a constant pressure...