Comparative Morphological Features of Syrinx in Male Domestic Fowl Gallus gallus domesticus and Male Domestic Pigeon Columba livia domestica: A Histochemical, Ultrastructural, Scanning Electron Microscopic and Morphometrical Study

Many studies have been carried out to investigate the morphological structure of the syrinx in many bird species. However, the cellular organization of the syrinx in the fowls and pigeons is still unclear. The current study revealed that in fowl and pigeon, the syrinx is formed of three main parts including tympanum (cranial) part, intermediate syringeal part, and bronchosyringeal (caudal) part, in addition to pessulus and tympaniform membranes. A great variation in the structural characteristics of syrinx of fowl and pigeon was recorded. In fowl, the tympaniform membranes showed a characteristic distribution of elastic and collagen fibers which increase the elasticity of tympaniform membranes. Moreover, the bony pessulus helps the medial tympaniform membranes to be stiffer, vibrate more strongly so that louder sound will be generated. In pigeon, the lateral tympaniform membrane is of greater thickness so that the oscillation of this membrane is reduced and the amplitude is lower. Moreover, the pessulus is smaller in size and is formed mainly of connective tissue core (devoid of cartilaginous or bony plates), resulting in the failure of stretching and vibrating of the medial tympaniform membranes, that leads to the generation of deeper sound. Electron microscopic examination of the syringes of fowls and pigeons revealed numerous immune cells including dendritic cells, plasma cells, mast cells, and lymphocytes distributed within syringeal mucosa and invading the syringeal epithelium. Telocytes were first recorded in the syrinx of fowls and pigeons in this study. They presented two long telopodes that made up frequent close contacts with other neighboring telocytes, immune cells, and blood capillaries.