rostrum(redirected from nasal rostrum)
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(1) In fish, the anterior part of the neurocranium, located in front of the olfactory capsules. The rostrum is especially prominent as an integral cartilaginous process in Acipen-seridae, for example, in the stellate sturgeon (Acipenser stellatus) and Scaphirhyncus, and in chondrichthians, for example, in the sawfish and saw shark. In the smooth hound and other fish the rostrum is represented by three separate outgrowths. In the sawfish and saw shark large cutaneous teeth (placoid scales) are located along the sides of the rostrum; in these animals, the rostrum resembles a saw and serves as a weapon of defense and attack. In the majority of Batoidei the anterior edges of the pectoral fins are attached to the rostrum. The rostrum is reduced in many contemporary bony fishes and in terrestrial vertebrates.
(2) In reptiles and birds, the anterior process of the basisphe-noid bone. The rostrum is formed by the concrescence of the integumentary sphenoid bone to the basisphenoid bone.