The objective of this work was to study the histological structure of the dog's coronary artery by light and transmission electron microscope (TEM). The coronary artery consisted of three tunics: tunica intima, tunica media and tunica adventitia. The tunica intima consisted of endothelium rested directly on internal elastic lamina without the subendothelial connective tissue layer. The tunica media were composed of smooth muscle fibres interspersed with few elastic and collagen fibres. The tunica adventitia consisted of collagen and elastic fibres intermingled with fibroblast cells; it had vasa vasorum and nervi vasorum. Some histomorphometric measurements were performed and compared statistically. The ultrastructural study showed that the endothelial cells were communicated through complex junctions and characterised by filiform cytoplasmic processes passed through the opening of the underlying internal elastic membrane. The smooth muscle fibres of tunica media communicated with each other through cytoplasmic processes. The tunica adventitia showed minute non-myelinated nerve. This work revealed that the dog's coronary arteries are typical muscular arteries, which show little structural variations from that of other mammals. K E Y W O R D S coronary arteries, dog, histology, transmission electron microscope, tunica intima | 81 KILANY et AL.

Retroperitoneal lymph node dissection for residual masses after chemotherapy is a high-morbidity procedure, even by experienced surgeons, although it remains an efficient modality of treatment in advanced germ cell carcinoma. The high frequency of tumor found in the RPLFN following chemotherapy might have been caused by the small number of patients in this study.

Ultimobranchial body (UBB) remnant was considered as an enigma till the last few years, then it was recognized as a necessary organ where it is the origin of the parafollicular cells. The samples were fixed and processed for the histological and electron microscopic examination. Macroscopically, the UBB remnant appeared as a white mass at the end of the cranial one-third of the thyroid lobe. It was composed of solid cell nest, cluster of cells and small thyroid follicles. Transmission electron microscope showed some round cells containing euchromatic nuclei, numerous parafollicular cells with darkly stained granules and paler ones. It also showed some mast cells with heterochromatic nuclei and large darkly stained granules. The parafollicular cells were distributed throughout the thyroid gland but concentrated within the UBB remnant.To our knowledge, our findings represent very unique histological manifestations specially the ultra-structural ones which revealed an original finding about the new clear type of cells suggested to be a UBB remnant and ensure those of the light microscope.

An investigation of the performance of pilot operated hydraulic relief valves has been carried out. The valve behavior is described by means of a nonlinear mathematical model, considering the nonlinear variation of the restriction areas, the nonlinear flow-pressure relations and the flow forces. The theoretical treatment is carried out by treating the developed mathematical model using a digital simulation program. The model is validated in the steady state by comparing simulation and experimental results. The transient behavior of the valve is investigated theoretically. The effect of the dimensions of the damping orifices and volume of oil filling the inlet line is predicted. The simulation program is used to predict the optimum dimensions of the damping orifices, which introduced an observable improvement in the transient response. NOMENCLATURE at Pilot valve poppet area sullected to pressure Pz, m 2. az Pilot stage opening area, m2. a Main poppet opening area, m. A Main poppet area subjIcted to pressure P, m At First orifice area, m Az Second orifice area, T k A3 Third orifice area, m. z At Area of the throttle valve, m B Bulk modulus of oil, N/m z. Cci Contraction coefficient. Cez Contraction coefficient. Ca Discharge coefficient of the valve opening orifice. Cat Discharge coefficient of the first orifice. Cd2 Discharge coefficient of the second orifice. Cd3 Discharge coefficient of the third orifice. Cd4 Discharge coefficient of the pilot stage restriction. D Main poppet diameter, m. dp diameter of the seat of pilot valve poppet, m.

This paper deals with the static and dynamic characteristics of a pressure compensated flow control valve. A nonlinear mathematical model of the valve is developed. The simulation of the valve is carried out using a digital computer on the basis of the developed mathematical model. The validity of the models is verified in the steady state by comparing simulation and experimental results. The dynamic characteristics of the valve are predicted theoretically using the simulation program. The influence of some constructional parameters on the valve Static and dynamic characteristics is investigated and optimum values of these parameters are determined. NOMENCLATURE Aa Area of the 1 st nd damping orifice, 2. A5 Area of the 2 damping orifice, m 2 1 Ap Spool area subjected to pressurl, m. At Throttling area of the valve, m. b Compensating stage opening, m. B Bulk modulus, MPa. Cc Contraction coefficient. Cd DAfcharge coefficient. cll 1 nd damping orifice diameter, m. dz 2 damping orifice diameter, m. dp Spool diameter, m. f Coefficient of viscous friction, NS/m. k Spring stiffness, N/m. m Spool and spring reduced mass, kg. Pi Input pressure, MPti. Pa Pressure in the 1 9 chamber, MPa. Pa Pressure in the 2 nd chamber. MPa.